A method for measuring speed of a permanent magnet synchronous motor includes: acquiring a number K of pulse signals received in a current measuring period and outputted by an incremental encoder; acquiring a first duration Sn-1 between a time point when a pulse is last received in a previous measuring period and a time point when the previous measuring period ends, and a second duration Sn between a time point when a pulse is last received in the current measuring period and a time point when the current measuring period ends; calculating a third duration T0, measured between the time point when the pulse is last received in the previous measuring period and the time point when the pulse is last received in the current measuring period, according to the length T of the current, measuring period, the first duration Sn-1 and the second duration Sn; and calculating a motor speed v according to formula: v = K K 0 × 1 T ⁢ ⁢ 0 .