To solve the problems of the major kinds of microwave radars to meet the ranging needs of vibrating constructions, a new type of radar system for ranging is proposed based on the carrier modulation and heterodyne phase difference detecting with time-to-digital converter (TDC). In the radar system, an intermediate frequency (IF) signal is used to modulate the amplitude of radio frequency (RF) carrier signal to produce transmitting signal, and radar system receives the back-reflected signal from the target and demodulates the IF signal to expand the unambiguous range. Then, the heterodyne processing and phase detector with TDC device are adopted to detect phase shift of IF signal for ranging to improve the ranging resolution and ranging speed. In addition, the ranging experiment results proved the feasibility and validity of the presented radar system.