The dynamic model of the 3PSS parallel mechanism was built using Lagrange equation. The driving force required of the sliding block of the 3PSS parallel mechanism was solved using Matlab software and the curve of driving force changing with time was mapped using Matlab in the case of the moving trail and the load of the moving platform were known. The validity of the Lagrange dynamic model of the 3PSS parallel mechanism was verified through the dynamic simulaton of the 3PSS mechanism in ADAMS software. Providing a theoretical basis for the design of the control system of the 3PSS parallel mechanism and laying a foundation for the further dynamic performance optimization.