Abstract: A time-to-digital convertor (TDC) based on field programmable gate array (FPGA) was designed for the cosmic ray μ measurement experiment. The high-precision time provided by TDC and a coordinated universal time (UTC) timestamp from GPS were used to make an accurate record of particle event. The method combining a coarse counter with a dynamic range larger than 1 s and a fine time interpolation based on FPGA carry-in delay chain was adopted in the TDC. The Wave-Union method and bin-by-bin method were used to improve the time resolution and linearity. The measurement results show that the time resolution of a double-edge TDC is 16.68 ps, the time measurement accuracy (RMS) is better than 45 ps, and TDC is sufficient for the pulse leading edge time discrimination.