HgCdTe avalanche photodiode （APD） is the frontier research on infrared focal plane technology. High-precision time stamp''s 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 device at low temperature， we design a vernier TDC circuit， which uses a synchronous counter to quantize an integer multiple of the periods to achieve a coarse count of 6 bits. We use the high-frequency clock multiplied by the on-chip phase-locked loop 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， and our circuit works at a master-frequency of 120 MHz. At 77 K， the circuit tests can distinguish the time resolution of 236.280 ps. The DNL is within -0.54~0.71 LSB， and the INL is within -1.32~1.21 LSB.