Abstract: A time-to-digital converter (TDC) with high precision based on field programmable gate array (FPGA) was presented in this paper. The method combining coarse counting and fine time measurement was adopted in the design. The coarse counting depended on a good performance binary counter and the fine time measurement was realized by using a fast carry chain to implement the time interpolation. For improving measure resolution, the method of Wave-Union was also employed in the design to divide the ultra-wide bin width. Various tests were implemented to check the performance of TDC, and some excellent results were achieved. The test results show that the time resolution (FWHM) of TDC is less than 50 ps within a wide dynamic range greater than 200 ms. The differential non-linearity (DNL) is in the range of -1-1.5 LSB, and the integral non-linearity (INL) is in the range of -1.5-1.5 LSB. The TDC will be used in In-beam position emission tomography (PET) equipment for time-of-flight measurement.