In order to measure the time interval with high precision, a time-to-digital converter based on Field Programmable Gate Array (FPGA) was designed. The whole system is divided into two parts: “crude” measurement module and “fine” measurement module. The basic principle of the “rough” measurement module is the direct counting method. The “fine” measurement module uses the carry chain inside the FPGA to construct the delay chain. In this paper, the delay module is optimized by the method of position constraint and multi-chain joint measurement. Finally, the physical test shows that the measurement resolution of TDC is 6.757 ps, the measurement accuracy is 33.802 ps, the range of differential nonlinear DNL is (-1, 3.322) LSB, and the range of integral nonlinear INL is (-11.055, 9.594) LSB. This technique can be used to calibrate the delay time of photoelectric signal transmission.