通过分析预警系统的预警步骤来探讨影响获得预警时间的因素，并与瑞士地震台网预警延迟各步骤进行对比，得出中国地震预警系统仪器延迟时间为7.6s。提出地震波到台站所需时间的算法，较震中假设在台站中间的传统算法更为准确，在此算法下采用双台法和四台法计算接收地震波所需时间，得到中国地震预警延迟时间。讨论双台法和四台法在不同震源深度和台站密度下对预警盲区大小的影响，在台间距小于20km时，2种方法预警盲区差异不大。通过理论计算得出，在台站到达一定密度时，预警系统仪器延迟时间缩短比台站加密对预警盲区的缩小更有效。

This paper analyzed the steps of the early warning system to obtain the influencing factors of the early warning time. By comparing with the early warning delay decomposition of the Swiss Seismic Network we obtain that the instrument delay time of the earthquake early warning system is 7.6s in China. In this paper we present an algorithm of seismic wave arrival time,which is more accurate than the traditional algorithm with the epicenter assumed to be in the center of the station. Under this algorithm,the time required for receiving seismic waves by the two-station method and the four-station method is calculated to obtain the delay time of earthquake early warning in China. We discuss the influence of the two-station method and the four-station method on the size of the early warning blind area under different focal depths and station densities. We find that when the interval between the stations is less than 20km,the difference between the two methods of early warning blind area is not significant. Through theoretical calculation,when the station density reaches a certain density,the instrument delay time of the early warning system is shortened,which is more effective than the station encryption to reduce the warning blind area.

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江苏省科技支撑计划—社会发展项目（BE2016804）、江苏省地震局青年科学基金（202102）共同资助