It is impossible to measure the M² factor of pulsed laser effectively by using the traditional equipment. For real-time measurement of the M² factor,two crossed defocus gratings and a lens with short focal length are used to obtain nine beam spots of different positions. The value of M² factor is determined by calculating the beam waists using the second-moment method and curve-fitting. According to the theory of Gaussian beam propagation and transformation,measured errors as functions of beam waist and positions are analyzed. The analysis shows that the measuring system can work well in a large range. The pulse-to-pulse M² factors and the change of M² factors along with the pumping voltages of the 1064 nm Nd:罽AG pulsed laser are measured. The results indicate that measurements of M² factor of pulsed laser are realized and the system can work successfully for measuring changes of M² factors during laser working in real time.