In order to analyze the periodic unsteady flow problem efficiently the partially implicit harmonic balance (PIHB) method was developed. Contrary to the existing harmonic balance method, this method handles the harmonic source term explicitly and deals with flux terms implicitly. This method has a good convergence in comparison with the full explicit harmonic method and it is easy to apply this method because there is no need to calculate the complicated flux Jacobian term by comparing with the full implicit harmonic method. With the multigrid method about the each harmonic it turns out that this method has a good convergence regardless of the number of harmonics. The oscillating flows over NACA0012 airfoil is considered to verify this method then the result correponsed to both the result of dual time stepping and explicit Runge-Kutta method.