High resolution time measurement system was implemented in a single FPGA based on time interpolation. On the basis of analyzing the principle of traditional digital counting method and its error, from the sight of error source, the fine time is the time difference between rising edge of the measured signal and next rising edge of counting clock, in order to measure the fine time accurately, we proposed a method that measures it with 4 interpolation clock signals, which have the same frequency and phase difference of 45 degrees in turn, estimating the fine time by latch clock state at rising edge of the signal to be measured. Meanwhile, a highspeed clock is used to measure the coarse time directly. The principle error of this method is discussed in detail. The experimental results show that this method can achieve a precision of 312.5 ps and the error less than 300 ps. The design has advantages of large measurement range, high accuracy, small size, and with less resource.