Abstract: This paper studies the TIP, that is the probability increase time of the strong earthquakes occerrence, existing in North China area since 1979 by modified M₈ algorithm.The result shows that 7 of the8 moderately strong earthquakes occurred in Probability increase time, the TJP warnings.makes up 40.7% of the studied total time-space domain, the evaluated point of R is.0T468, objaining a relativelygood mid-term prediction effect of moderately strong earthquakes, which indicates that this metbod canbe used as one of mid-term prediction means of moderately strong earthquakes., in lage North Chinaarea.