Abstract: Two way satellite time and frequency transfer technique is a fundamental means of high precise time and frequency comparison, with which A type uncertainty is about 0.1ns in time comparison. The B type uncertainty is mainly relies on the system calibration. In this article, the principals of two way satellite time and frequency transfer is firstly review. Then various existing techniques and devices for TWSTFT calibration are presented in detail. Their performances and characteristics are compared and reviewed. The development of the calibration is concluded and the future trend is discussed.

Key words: Two Way Satellite Time Frequency Transfer , Delay calibration, Satellite simulator