Abstract: A new approach-entire equivalence current integral equation is developed for the analysis of microstrip antennas. The equivalence principle is used to describe the effects of all conducting bodies by equivalent surface electric currents and all dielectrics by equivalent volume polarization currents, which we call entire equivalence electric current integral equations (E 3CIE). Moment methods (MM) are utilized to solve the electric current on the entire structure. Any kind of microstrip antennas can be analysed using this approach, and the effects of the finite size ground plate is considered in analysing. The salience of this approach is that free space Green's function is used instead of spectral or spatial Green's function, avoiding the difficulties of infinite spectral integral or Sommerfeld integral. Finally, typical results of rectangular microstrip antenna are presented and compared with other's, validating this approach.