It is chosen as research object that joint robot arm avoids erect stem or strut to pick tomatoes, and a kind of obstacle-avoidance path planning method based on configuration space of joint robot arm was presented. Space mapping principle was used to transform obstacle-avoidance problem of joint robot arm in 3-D workspace into avoiding obstacle circle problem of planar R-R robot arm. Critical collision joint angle was used to build up mapping computation models of configuration obstacle space of planar R-R robot arm, and obstacle-avoidance position computation of joint robot arm in 3-D workspace was transformed into joint angles computation of linkages in configuration space. After terminal joint angles of obstacle-avoidance path planning were optimized according to optimal energy function, the obstacle-avoidance joint angle path of planar R-R robot arm based on A* arithmetic was computed. A series of intersectant erect planes described space link position were obtained and the planning of other joint was carried out in the intersectant erect planes. The test of avoiding erect obstacle to pick tomatoes showed that joint robot arm carried with the gripper can move round linear obstacle and guide the gripper to reach object position. The test proved that mapping computation models of configuration obstacle space of planar R-R robot arm were correct. It validated that the obstacle-avoidance path planning method was feasible and may be applied into automatic harvesting of tomato. 