Abstract: High order hierarchical bilinear basis function is proposed to reduce the number of unknowns for the method of moments(MoM) analysis on the electromagnetic scattering of dielectric objects. It combines higher-order vector basis function with bilinear basis function, and is employed to solve the Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) equation. The number of unknowns and the accuracy are compared between the new basis functions with different orders. Numerical examples show that the proposed method requires relatively less unknowns than the conventional method, and can obtain the same precision.