Abstract: This study aims to meet the application requirements of unmanned driving and autonomous operation in agricultural machinery, particularly for better adaptability of quadrilateral farmland. A path planning was also designed to implement the farmland operation using unmanned agricultural machinery. AB line operation mode was selected to generate executable paths with speed and implement state instructions. Two parts were composed of farmland information processing and path planning. The farmland information processing module was used to process the surveying point data in land contour and obstacles. Among them, one data processing was for land contour surveying and mapping points, and another for obstacle surveying and mapping points. The former was used to extract the longitude and latitude fields of original position data, and then convert them into Universal Transverse Mercator (UTM) coordinates. The latter was utilized to convert the point and line obstacles generated by surveying and mapping into the unified obstacle polygonal contour data for the subsequent path planning. Next, the operating parameters were defined by the user in the path planning module, including the operating direction, operating width, turning radius, and starting position. The sub-modules were also constructed, such as unmanned operation trapezoidal area generation, turning and operation area division, operation strip segmentation, obstacle strip processing, strip routing planning, turning, and final path generation. The research methods were as follows: (1) In the sub-module of unmanned operation trapezoidal area generation, the operation direction was taken as the parallel side to construct a trapezoidal area suitable for unmanned operation in the quadrilateral land. (2) In the sub-module of turning and operation area division, the width of the turning area was set, according to the operating width and turning radius. Then, 2 parallelogram turning and 1 operation area were generated inside the unmanned operation trapezoidal areas. (3) In the sub-module of operation strip segmentation, the operating direction was taken as the strip direction, while, the operating width as the strip width, in order to complete the strip dividing of the entire operation areas. (4) In the sub-module of obstacle strip processing, the operation line was cut to intersect with the obstacle polygon back and forth, and thereby to construct a detour path composed of arcs and line segments. (5) In the sub-module of strip routing planning, the operation strips were sorted in order. All the strips were divided into the blocks with constructing units, while, the strip selection was designed for different operating sequences to achieve better orderly operation strips. (6) In the sub-module of turning path generation, a U-shaped turning path was generated in the form of "arc-line-arc" using the adjacent sequence of operation strips and turning radius. (7) In the sub-module of final path generation, the final path was realized by adding speed instructions and implement state instructions at the path points. The final path was thus executed in the unmanned agricultural machine. Simulation tests show that the proposed method was suitable for different quadrilateral farmland and obstacles. The operation area ratio and distance ratio increased by 10.0% and 8.8%, respectively, compared with the adjacent. Field tests show that the mean value and standard deviation for the lateral deviations of agricultural unmanned driving and autonomous operation were 0.002 m to the left and 0.027 m, respectively. Consequently, the generated path can meet the requirements of unmanned and autonomous operation in agricultural machinery. The finding can provide a complete path planning for unmanned agricultural machinery with the high adaptability of farmland and operating parameters for higher production efficiency.