Quantum Interference Radar (QIR) is a new radar regime based on quantum mechanics and exploits the quantum entanglement effect for target detection, and the variation in the number of photons detected by QIR has an impact on the radar resolution and system survival function. In order to reduce the influence of the liquid water content of stratocumulus on the detection performance of the QIR system, the optimal average photon number adaptive algorithm(Photon Number Adaptive Algorithm, PNA) based on the decoy state quantum key protocol is proposed. The relationship between the liquid water content of the stratocumulus, the transmission distance and the optimal average photon number is established, and the QIR resolution and the system survival function before and after the adaptive adjustment are compared. The theoretical analysis and simulation results show that when the pulse wavelength is fixed,the stratocumulus particle concentration is 1. 579×104 cm-3, and the stratocumulus liquid water content is 0. 5 g/ cm3,the QIR angular resolution decreases from 1. 289 to 1. 028 after adopting PNA strategy, and both the angular resolution and spatial resolution of the QIR system are effectively improved. when the liquid water content of stratocumulus is 0. 103 4 g/ cm3, the channel survival function improves from 0. 229 2 to 0. 416 7. Therefore, the reliability of QIR detection in stratocumulus can be improved by adaptively adjusting the average number of photons contained in the signal pulses of the sending end of the system through PNA strategy.