The basic principle and the composition of the additional digital timing function of the existing Loran-C system are introduced, and the influence of the main error source on Loran-C timing accuracy is also estimated. On the basis of the test for the transmit stations on site and outdoors, the satellite common view error, the time transmission control error as well as the timing deviation of receiver under self-position and non-self position mode are presented, and the timing accuracy of the test is also analyzed.