To suppress the effects on orchard tree canopy measuring of uneven ground and deviation in driving path from the centerline between two rows, RTK-DGPS and AHRS (attitude heading reference system) were used with ultrasonic transducer array to obtain the three-dimension data in terms of the geodetic coordinates of each detected point on the tree canopy through rotations and translations of relevant coordinate system. 3-D reconstruction and volume measuring of fruit tree canopy were conducted on a PC with matlab software. The structure and work theory of the measuring system were introduced in detail. Experiments were conducted in lichee orchard, where 15 trees with different heights and canopy volumes were measured three times using the designed system. Another 56 trees were measured by the system and manual method separately and their results were compared. Experimental results showed that the repeatability of the system was high (R2=0.9341, RMSE=1.22 m3), and the calculated volume results were consistent with manual measurements (R2=0.8972, RMSE=1.766 m3). The effectiveness of this method indicates that the designed system can be used in 3-D reconstruction and the canopy volume measurement of trees in orchard.