Compared to traditional RSOA, the reflective quantum dot semiconductor optical amplifier (R-QDSOA) has the picosecond carrier recovery rate and the modulation bandwidth of dozens of GHz. It is reveal that R-QDSOA has a great application prospect in high-speed WDM-PON. The simulation model of R-QDSOA is built according to the carrier rate equations and the light field transmission equations. And then the high-pass properties under the condition of gain saturation are investigated. The results show that the maximum signal gain and 3dB cutoff frequency can be improved by increasing the input optical power, maximum mode gain, active area length and reducing the injection current; the 3dB cutoff frequency of the R-QDSOA can achieve larger than 10GHz with reasonable parameter. This research makes R-QDSOA a promising candidate for re-modulation scheme of colorless WDM-PON and has theoretical significance for improving the modulation bandwidth of R-QDSOA.