A composite sliding mode control method, which was based on the traditional double power sliding mode reaching law method, was adopted for the requirements of low chattering, high-performance and strong robustness on the motion platform of permanent magnet linear synchronous motor precision laser cutting. A variable boundary layer of double power reaching law with sliding mode disturbance observer has been proposed in this paper. The method of variable boundary layer is a trade-off between control precision and chattering reduction, and it inherits the finite time convergence properties of the double power sliding mode reaching law. In order to reduce the conservatism of the system design, a sliding mode disturbance observer based on super-twisting algorithm was used to estimate the unknown disturbance on the system. A power exponent was added in this algorithm and the simulation experiments verified that increasing the value of the power exponent can accelerate the convergence rate of the unknown disturbance estimations. The stability of the closed-loop system was proved by the Lyapunov stability theory. Finally, a laser cutting translation test stage based on PMLSM was built. The experimental results showed that the proposed control method could satisfy the requirements of the system.