In this paper, 16 items of 4 factors used in distinguishing magnitude interval related to maximum event that might happen every year are chosen, and the earthquake sequences of M_s≥4.0 (in exception of aftershock) occurred in North China from 1960 to 1986 are dealt with. Fuzzy relation equation of magnitude decision containing 3 magnitude intervals, M_s≤6.0, 6.0s<7.0 and M_s≥7.0 are given. Seven event examples are used to inspect the prediction result of this equation. The result indicates that all of them passed through prediction inspection. This paper also made a estimate that maximum event of which magnitude would be M_s≤6.0 might occur in North China in 1987.