Analysis model containing two inclined surface cracks on semi-infinite elastic body is established and analyzed on the basis of linear fracture mechanics to examine mutual interference of two surface cracks. Muskhelishvili's complex stress functions are introduced and a set of singular integral equations is obtained for a dislocation density function. The stress intensity factors at crack tip are obtained by using the Gerasoulis'method. When two surface cracks are parallel and have the same length, the values of $\small{K_1}$and $\small{\Delta K_11}$(variation of $\small{K_11}$) for crack 1 and crack 2 decrease by the mutual interference of two surface cracks as the distance between the two surface cracks shortens. The effect of mutual interference is remarkable in high friction coefficient. In case that two surface cracks are parallel, the values of $\small{K_1}$and $\small{\Delta K_11}$for crack 2 decrease as the length ratio ot crack 2 to crack 1 becomes small. As the crack inclination angle rises, the value of $\small{K_1}$ and the mutual interference of $\small{K_1}$for crack 2 increase and the value of$\small{\Delta K_11}$ for crack 1 becomes smaller than that for crack 2.