The acetabular cartilage plays an important role in hip joint biomechanics and many reports focusing on its geometric morphometry have been made, but few studies have done some sensitivity analysis to figure out the impacts of geometric shape parameters on hip contact stress. This paper aims to elucidate how the length ratio of the rotational ellipsoidal acetabular cartilage surface's major axis to minor one (ALR) affects the contact stress in the hip, via analyzing finite element (FE) models of hip mechanics with varying ALR. By using the reverse engineering technique and surface-fitting algorithms, 11 best-fit rotational ellipsoidal surfaces of the point clouds from a volunteer's right acetabular articular surface with different ALR (from 1.00 to 1.20) were created. The contact stress between a sphere (femoral head surface) and 11 best-fit rotational ellipsoids (acetabular cartilage surfaces) with a hip contact force (Bergmann et al., 2001) applied on femoral head centre was calculated, via FE analysis technology and the ANSYS software. As the ALR grew from 1.00, it was found that the surface fitting error of this specimen decreased to reach its minimum at 1.156 (23.9% lower than standard sphere), and then increased gradually. A similar trend was observed from the corresponding contact stress results. These results support the idea that the more the model geometry morphometry is similar to the natural human articular surface, the more excellent mechanical properties it tends to own.