High precision repeatability is the precondition of testing accuracy and also one of the most important parameters of high precision testing. In Fizeau interferometer, the interferometer cavity is sensitive to environments, especially to temperature variation. Temperature is also one of the main factors that influence the test repeatability. The interferometer cavity model is established based on Edlen equations according to light transmission theory. The theoretical analysis shows that the repeatability is mainly affected by the cavity length and the temperature variation. The repeatability variation is tested through ZYGO interferometer at different environments and different cavity lengths. The test and computation results are compared and analyzed.