1K-50 orchard ditching machine with the characteristics of compact structure and convenient operation and transfer has been developed to use in the low and narrow environment of orchards in southern China, which operated in the way of double rotary tillage wheel structure and reverse rotary cutting of soil. In the application process of 1K-50 orchard ditching machine, it was found that the machine could meet the requirement of maximum ditching depth 0.5 m in orchards with small soil solidity, while in vineyards with large soil solidity, the maximum ditching depth was about 0.2 m, and there was aggravated machine vibration. It is necessary to explore the factors which have an effect on the process of cutting and throwing soil, and then optimize the working parameters and structural parameters of the knife roller. In this paper, a mechanical model of cutting, transporting and throwing soil was established to analyze the power consumption of the ditching parts, and obtain the functional relationship between the power consumption of the ditching parts and the working parameters of the whole machine, the structural parameters of the knife roller and the mechanical properties of the soil. A testing device for power consumption of trenching components based on soil tank test bench was built to simulate the soil environment of vineyard with the solidity of 950 kPa. Roller speed, forward speed, ditching depth and type of the knife roller as test factors were selected, and effects of the factors on power consumption were studied under different structural parameters and working conditions by the single factor test, and four-factor and three-level orthogonal experimental design. The factors affecting power consumption of ditching components in order were the type of knife rollers > forward speed > speed of knife rollers > depth of ditching. Through range analysis of data, the optimal combination of parameters for power consumption was obtained by the D3 type knife roller, the speed of the knife roller of 150 r/min, the forward speed of 0.06 m/s and the ditching depth of 0.15 m. Under the optimal combination parameters, the average power consumption of the ditching parts is about 1.22 kW. The horizontal values of each group of test factors in the orthogonal test table were substituted into the power consumption analytic formula. The power consumption values were calculated numerically by using the software of MATLAB, and the range analysis was carried out. The primary and secondary order of the factors affecting power consumption was the same as that of the bench test results. Under the same conditions, the power consumption between the numerical calculation values and the bench test values were obtained. The maximum and the minimum relative errors were 12.86% and 2.00% respectively. It verified that the theoretical model of power consumption had high accuracy. The research can provide the reference for improving the machine and designing the small-scale trencher in forest orchard.