Picking manipulator ontology structure used rotation and translational motion pairs to join the components together, and then a multi-joint motion mechanism was built which meet the picking space requirement. According to the characters of growth space of litchi fruit, here used helix transmission as the first axes of the picking manipulator, to achieve motion in vertical direction. This study introduces the application of multi-domain modeling and simulation when constructing and simulating a helix transmission. Use object-oriented technology, multi-domain modeling and simulation language Modelica to construct the motion system which integrates motor model, signal detection module, signal processing module and parametric screw transmission model in Dymola simulation platform. Test the helix transmission by simulation, using the mechanical structure, sensor technology, signal processing technology. Simulation results show that, the modelica can provide a valid simulation for complex electromechanical system and support for parametric design.