Provided is a free piston generator based on a split thermodynamic cycle, which belongs to the technical field of power energy. The present disclosure solves the problem of low power generation efficiency of an existing free piston generator. The free piston generator includes a linear generator set and two internal combustion engine sets arranged at two ends of the linear generator set. Air is first subjected to first-stage compression by the low-pressure cylinder set in the internal combustion engine sets and is then subjected to second-stage compression in the high-pressure cylinders, so that the intake pressure of an internal combustion engine is effectively increased, which is favorable for increasing the average effective pressure in a work process, thereby improving the thermal efficiency and the power generation efficiency of the free piston generator. A combusted working medium is first subjected to first-stage expansion in the high-pressure cylinders and is then subjected to second-stage expansion in the low-pressure cylinders, which effectively increases the utilization rate of energy in exhaust gas, increases the expansion work, and further improves the thermal efficiency and the power generation efficiency of the free piston generator.