HgCdTe avalanche photodiode (APD) is a frontier research on infrared focal plane technology, High-precision time stamp readout circuit is the basis of the APD focal plane at 77 K, which directly affects APD infrared focal plane performance. Time-to-digital conversion circuit (TDC) is one of the methods to achieve high-precision time stamping. Based on the analysis of MOSFET at low temperature, our design a vernier TDC circuit, which uses a synchronous counter to quantize an integer multiple of the period to achieve a coarse count of 6 bits; The on-chip PLL multiplied high-frequency clock has high-precision and high PVT characteristics, using it to quantify the part that is less than one clock cycle to achieve a fine-count of 6 bits output. The circuit adopts standard CMOS process tape out, our circuit works at a master-frequency of 120 MHz. At 77 K, the circuit test can distinguish the time resolution of 236.280 ps. The DNL is within -0.54~0.71 LSB, and INL is within -1.32~1.21 LSB.