In order to study the characteristics of temperature field and stress field of fused silica irradiated by millisecond-nanosecond combined pulse laser, based on the theory of heat conduction and elastic-plastic mechanics, two dimensional axisymmetric geometric model was established, the numerical simulation software was used to analyze the process that fused silica irradiated by millisecond-nanosecond combined pulse laser. The temporal and spatial distribution and variation of the transient temperature field and stress field on the surface and inside of fused silica were obtained. The result shows, in the combined pulse laser, the millisecond pulse width is 1 ms, the energy is 120 J, the nanosecond laser pulse width is 10 ns, the energy is 80 mJ, Δt=1.0 ms, the best time delay for the temperature of fused silica irradiated by millisecond-nanosecond combined pulse laser, according to the different energy ratio of millisecond and nanosecond, the thermal effect of millisecond pulse laser on fused quartz and the stress effect of nanosecond pulse laser on fused quartz are obtained.