We report the continuous wave (CW) second harmonic generation (SHG) with a periodically poled KTiOPO4 (PPKTP) pumped by a diode laser at 852.356 nm, which is exactly resonant on the cesium D2 transition. An output power of 54.4 mW of blue light at 426 nm was obtained at the pump power of 136.4 mW. The conversion efficiency is about 40%. The best matching temperature is 318.3 K. This CW blue light can be used for atomic physics, especially for the generation of nonclassical light at the transition of cesium atom through optical parametric oscillator (OPO).