Abstract: By establishing thin plate mechanical model of main roof with elastic foundation boundary and using the fi- nite difference theory,the paper studied the effect of elastic foundation coefficient k,main roof thickness h,main roof Young modulus E,the hanging roof length a1 ,the ratio k / E and k / h to the main roof primary bending moment and pe- riodic fracture regularity. It is concluded that with the increase of the E or h, the absolute maximum primary moment Md of short side and Mc of long side,and the maximum primary moment Md of suspended roof’s rear boundary all in- crease;while with the increase of the k,the primary moments Mc ,Mb and Md all decrease,and the decrease amplitude of the Md is the biggest. According to the fracture criterion of primary moment,the value of E,h or a1 is big,or the val- ue of k is small,the upper surface of the short side ahead of the coal wall first fractures,whereas the long side ahead of the coal wall first fractures;if the ratio k / E or k / h3 is unchanged,the primary moments Mc ,Mb and Md are unchanged and the initial fracture position of main roof is unchanged. The periodical fracture types of main roof with elastic foun- dation boundary are:① long side upper surface→short side upper surface→lower surface of suspended roof’ s rear boundary;② short side upper surface→long side upper surface→lower surface of suspended roof’s rear boundary.