Low frequency time-code timing service is an important mode in the modern timing system, and it is actively commended by International Telecommunications Union (ITU). Low frequency time-code timing radio station (BPC) is built by National Time Service Center in China. The BPC broadcasts are used by millions of people to synchronize consumer electronic products like wall clocks, clock radios, and wristwatches. In addition, BPC is used for high level applications such as network time synchronization and frequency calibrations. Based on the modern signal characteristic of low frequency time-code of BPC, the additional spread spectrum modulation timing method in idle carrier wave is presented. A new structure of signal modulation is expatiated. The rationale of the additional spread spectrum modulation timing method in BPC is researched. The performance of a new system error is analyzed. The research results indicate that the anti-jamming performance can be improved by the additional spread spectrum modulation timing method in BPC, and low frequency time-code timing service can then be used broadly.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.