Combining the structure characteristics of free-piston Stirling engine, a kind of dynamic displacement measurement that the strain gauge are used to measure indirectly the displacement of displacer and piston by responding to shape change of plate spring is put forward. On the basis of strain-resistance effect and bridge principle of strain indicator, a set of dynamic displacement measurement system based on strain gauge is built up, and experimental data are compared with the data gotten from static displacement measurement. The experimental testing results indicate the data from dynamic displacement measurement are not exactly the same as the data from static displacement measurement, and the attaching position of strain gauge directly affected the accuracy of measurement.