The free piston Stirling generator is composed of free-piston Stirling engine and linear generator. It has important application value in solar thermal utilization and cogeneration combined heat and power. A magnetic circuit structure was designed for the moving-magnet linear generator in the free-piston Stirling generator. The finite element software (Ansys/Maxwell) was used for simulation and analysis. A electromagnetic field model of this moving-magnet linear generator was established. The distribution of magnetic induction lines in different positions and the distribution cloud maps of magnetic induction intensity were obtained for the linear generator under no-load operation. It is found that the magnetic induction intensity at tooth tip is always the largest no matter where the actuator moves. Based on the simulation results, the induced electromotive force of the linear generator under no-load was calculated to be 111.22 V. The performance simulation of the linear generator under no-load is helpful to optimeze its design.