The parameters of the vector control system of surface-mounted permanent magnet linear synchronous motor (SPMLSM )are generally set in accordance with the nominal value offered by its producer, but there is a difference between the actual value of the motor and the nominal value, which prevents the system from doing optimal performance. The paper puts forward an on-line identifying method of the back electromotive force constant and quadrature axis and direct axis inductance of PMLSM. With the given linear velocity of the system, current controller output waveform can be measured and the correspondent Walsh coefficients of first order can be calculated. The parameters required by system setting are renewed until the Walsh coefficients converge to zero, and the back electromotive force constant and quadrature axis and direct axis inductance are measured on-line. The experiment findings of the vector control system show that the measured electromagnetic parameters can reflect the actual value correctly and improve the system’s dynamic performance.