In order to settle the problem of real-time and dynamic non-contact measuring the swing angle of scanning mirror, a method of laser dynamically measuring swing angle of scanning mirror for the infrared earth sensor based on laser measuring technology and CCD detecting technology is presented. System for dynamically measuring swing angle of scanning mirror is developed, which can accomplish the dynamic and static laser non-contact measurement for the parameters of scanning mirror which are swing frequency, angle of zero position, amplitude value, average of peak values, etc. The composition and overall structure of system is introduced. Emphasis on analyzing and discussing the theory of dynamically measuring swing angle of scanning mirror, the method of design for large field of view, large relative aperture and special linear scanning optical system, the problems of error correction for measured data and graph manipulation are settled by established mathematic model of the system. The accuracy of measurement system is verified by experiment, the results indicated that measurement range of system for swing angle is 0°～±12°, distinguishing ability of the system is 0.01°, accuracy of dynamic and static measurement is less than ±0.04°, this method of dynamically measuring swing angle is suitable.