The interband cascade infrared photodetector （ICIP） can achieve high operating temperature by using the multistage cascade absorption region. But different design of absorption region will cause the mismatch of photogenerated carriers， which will affect the quantum efficiency of the device. In order to better understand the influence of the stage and thickness of ICIP on quantum efficiency， we measure the performance of ICIP based on the type-II InAs/GaSb superlattice at different operating temperatures. And based on the “average effect” of photocurrent， a quantum efficiency model operating at reverse bias voltage is established. Compared with the measured results， it is found that the experimental data and the calculated results are in good agreement at low temperatures. It is verified that the photocurrent is the average of current at all stages based on the electrical gain. However， the experimental photocurrent at high temperatures is lower than the calculation. This may be due to the short minority carrier lifetime at high temperatures， and the photogenerated carrier recombination mechanism exists at the interface of the absorption region and the relaxation region.