In order to improve the applicability of the orchard operation platform, the target workspace according to the planting mode was determined. The kinematics model established based on D-H method was derived on the basis of prototype development. The dimension deviation, volume and average operability of the platform were calculated as the indexes to evaluate the performance of the reachable workspace simulated by Monte Carlo method. The influence of the platform structure parameter rod length and joint variables (joint angle and link offset) on these three indexes were analyzed. The optimization function established by taking the performance of reachable workspace and compact structure as the optimization index was transformed into a single objective optimization function by analytic hierarchy process. The optimal parameters obtained by genetic algorithm were as follows: the length of rod 2 was 988mm, the length of rod 4 was 879mm, the range of joint angle 1 was [107°, 256°], the range of joint angle 3 was [-118°, -76°], and the maximum value of link offset 5 and 6 was 720mm and 340mm, respectively. Compared with the prototype, the dimension deviation of reachable workspace was decreased by 96.09% and 95.60%, volume was decreased by 4.69%, average operability was increased by 1.43%, sum of rod length was increased by 4.85%, and sum of joint variables was decreased by 3.11%. A three-factor three-level test with the platform load, cross slope angle and longitudinal slope angle as factors was designed. After the field test of the prototype workspace at orchard, the test results showed that when the load was 65kg, the cross slope was 15° and the longitudinal slope was 15°, the deviation between the actual reachable workspace and the target workspace was 16.2mm and 16.7mm, which were reduced by 93.89% and 93.76%, respectively. The research result can provide a reference for the structural parameter optimization of similar agricultural machinery.