In studying the performance of a sequential turbo-charging engine and protecting the turbo-charger from over-speed, the real time measurement of the speeds of turbocharger and the engine is necessary. A new method for the measurement of revolution speeds was given. The analog signals of the speed sensor were read into the computer through a data acquisition card and the periods of the signals were recognized by time saving arithmetic calculations. It was found that the method provides feasible precision and satisfies the demands of performance research on sequential turbo-charging engine.