Abstract: Based on the analysis of observed stress data from 6 stations in North China area and by combining 1 eartlKjuakes of M ≥ 5 occurred in North China area in recent years, a study is made for the relationship between relative stress and earthquakes in North China area. It has been found that the moderately strong-earthquakes of M ≥ 5 in North China area have no clear relation with the variation of stress state at each single observational point, but have close relation with the variation of mean stress state of the whole region, such a relation is not only shown in the normal stress variation in different directions in horizonial space, but also shown in the shear stress variation in due eastwest direction and due north-south direction, the both play a leading role in the occurrence of sstrong earthquakes in North China area.