A non-delayed full link high precision internal calibration scheme of radar system based on built-in calibration module is introduced in this paper. By adding internal calibration module and necessary calibration signal coupling and separation circuit to the existing radar system, this scheme can realize the transmitting, receiving and reference calibration of the radar system in working condition with low cost and low system complexity. It has the characteristics of simple system composition, comprehensive calibration mode, large dynamic range of calibration signal, high precision calibration in full temperature range. It can be used as a feasible scheme for non-delayed calibration of radar system.