An aero-engine rotation speed sensor speed measuring motor outputs an AC voltage signal, the frequency of which is in direct proportion to the rotation speed of an engine; and by measuring the frequency or period of the AC signal, the rotation speed of a rotor can be obtained. Since the AC voltage signal output by the aero-engine speed measuring motor rises with the rotation speed, voltage change range is 0.1V-50V, and the maximum limit of the frequency variation range reaches 83.3 Hz (corresponding to the maximum speed 100% of the aero-engine rotor), the invention provides a method for measuring speed signal frequency based on a high-speed data acquisition card, wherein the method is characterized by collecting speed time-domain signals of the aero-engine rotor directly, setting trigger threshold, and calculating the time difference between rising edges of the speed time-domain signals to obtain rotating speed period of the rotor. Meanwhile, since the speed signals output by the measuring motor are not standard sine signals and have a certain clutter signals, and in order to remove clutters in the signals output by the aero-engine speed measuring motor, the invention also provides a method for carrying digital filtering processing on the signals.