This paper shows a thin ship theory of the wave making resistance considering an effect of the gradient of hull form in the depth direction based on linear approximation, which is made by modifying the original Michell's thin thip formulation and by using Havelock's Green function. Some computing applications of wave resistance by both Havelock's formula and pressure integration on the centerplane of the ship are shown to compare with other researchers' results. The effects of vertical gradient of the hull on wave resistance are the phase shift in Froude number domain and the decreasing amplitudes of humps and hollows in comparison with Michell's integral. We control the added depth gradient term to affect in low Froude number range by a condition. The present method must be improved further to enhance quality and reliability.