With the development of modern navigation, aerospace, communications, electric power, especially in the military field, the uniform standard time is becoming more and more important. The performance of time-frequency system reflects the comprehensive strength of a country's science and technology. The current representative high precision time service technologies are introduced in this paper, mainly including ground-based radio timing, satellite timing, optical fiber timing, etc. The advantages and disadvantages of high precision timing methods are summarized. Aiming at the concept of "time warfare" put forward by the US Army, discussing the application prospect of different time warfare technologies and the necessity of constructing optical fiber network time transfer system, the technical difficulties are analyzed