Theoretical study and numerical simulation were carried out on the newly proposed way of cascaded second harmonic generation (SHG) to get stable SHG output. The results certify that by way of using cascaded SHG one can obtain stable SHG output. Our results also show that by tuning the angle between k and the optical axis and the distance between the two SHG crystals, the length of the second SHG crystal for most stable SHG can also be tuned. When the length for most stable SHG is tuned to the real length of the second SHG crystal, stable SHG output was be obtained. Both stable SHG output and high SHG conversion efficiency can be got using this new way, and this will help a lot to design the pumping system for the optical pulse chirped amplifying system.