Based on the calculation formulas of heat treatment temperature field of the narrow strip spot of laser beam passing a scanning rotating mirror, the effect of scanning frequency on temperature field was analyzed in this study, and the math model of the temperature field with scanning frequency was derived applying the superposing principle of the temperature field. The value simulation and figures description were given. The relationship between scanning frequency and temperature distribution was studied, and the best extent of frequency was given for carbon steel laser quenching with laser rotating mirror. The value simulation shows that the higher the scanning frequency is, the more evenly distributed the temperature field gets. At a certain laser power and a certain length of laser scanning line spot, for non-melting laser heat treatment under the spot, a maximum thickness of the high- temperature layer can be get at some certain scanning frequency range which depends on thermal diffusion coefficient of the material.