In order to choose a better input coupler, the conversion efficiency of the frequency doubling cavity were studied in the case of the transmittance of the input coupler to the fundamental light of 5% and 10%, respectively. 447.3nm blue light was obtained by external-cavity frequency doubling of a tapered amplifier-boosted continuous-wave diode laser at cesium D1 line. The frequency doubling cavity consists of a two-mirror standing wave cavity with a periodically poled KTiOPO4 (PPKTP) crystal inside. With a maximum fundamental power around 350mW, the frequency doubling cavity with a 5% transmittance input coupler generate 178mW blue light, corresponding to a conversion efficiency of 50.8%. With the input coupler with a 10% transmittance at the fundamental wavelength, 131mW of blue light is obtained, and the corresponding conversion efficiency is 37.4%. With a maximum input fundamental power, the output blue power was measured for 0.5h. In the frequency doubling cavity with 5% transmittance input coupler, the root mean square fluctuation is 1.4%, while the other is 0.7%. The result shows that the input coupler with 5% transmittance is better. This research is helpful for preparing high quality pump light resources to generate nonclassical light at cesium D1 line．