The invention provides a surface mounted permanent magnet synchronous motor air-gap magnetic field analytic method. On the basis of an equivalent magnetic circuit model and a conformal transformationmethod, the method is implemented; by building the equivalent magnetic circuit model of a whole motor, magnetic permitivity parameters in the conformal transformation method is corrected, and meanwhile the magnetic saturation effect of a stator silicon steel sheet is considered in the process; therefore, the advantage that the air-gap magnetic field analytic calculation precision of the motor under different working conditions is achieved.