The invention relates to a method for continuously measuring the rotating speed of a main heat transfer pump in a nuclear island from reverse rotation to forward rotation. N inductance approach switches, a rotating speed signal processing unit and a signal modulator are used in the invention. The nuclear control of large foreign companies to the nuclear power field in China and the technology and price monopoly of key products are solved. The method can be popularized in the measurement of the rotating speed of other similar pump shaft pump groups to reduce imported products and improve the localization rate of nuclear power stations.