Through testing the detection process of infrared(IR) up-conversion step by step along with theoretical calculation, the IR response characteristics of the cascade IR up-converter(CIUP) and the whole up-conversion system were thoroughly studied. Test results show that CIUPs can achieve considerable IR responsivity under weak background luminescence. The responsivity of the CIUP rises very fast under the flat-band bias and the conversion process from IR light signal into CIUP′s electrical signal displays excellent linearity. By applying the ABC model to the near-infrared radiation process of the CIUP, the fitted response current of the up-conversion system and the fitted current conversion efficiency agree well with the measured data, which gives a reasonable explanation for the non-linearity of the system′s IR response.