This paper presents a calculation method for the 3-D unsteady sheet cavitating hydrofoil problem. The method is based on a simplified surface panel method “SQCM”. Hess and Smith type source panels are distributed on the hydrofoil and cavity surfaces. Discrete vortices are distributed on the camber surface according to Lan's QCM (Quasi-Continuous vortex lattice Method). The boundary conditions to determine these singularities are the constant pressure condition on the cavity surface and the zero normal velocity condition on the hydrofoil and camber surfaces (except the trailing edge). We consider the unsteady Kutta condition that the pressures must coincide with each other on the upper and lower surfaces at the trailing edge. Then we introduce the normal velocity at the trailing edge. This normal velocity is obtained by iteration for the equal pressure condition. The cavity shape in each spanwise section is determined so that the zero normal velocity condition is satisfied on the cavity surface. In the present method, a cavity length for each spanwise section is given first. Then the singularities and the cavity shapes are determined. The cavity length is corrected in order that the opening at the cavity end will get closer to the target value. By using the corrected cavity length, the calculation is repeated from the beginning. These steps are repeated until the opening at the cavity end agrees with the target value in each section and then we move to next time step. This method is applied to the Wagner problem, heaving hydrofoil and a hydrofoil in a sinusoidal gust. We show some calculated results for partially cavitating and super cavitating hydrofoil and compare them with another calculated results.