In view of the problem of solar radiation in the imaging spacebased laser warning system, the effects of sunlight on the infrared detector of warning system were studied by theoretical analysis and numerical calculation. On the basis of analysis of the different spatial relationship of sun and detector, the influences of direct sunlight and sunlight reflected by earth to the signal to noise ratio(SNR) of infrared image, laser threat detection, the detector safety were investigated respectively. The results show that the sunlight is the mainly background radiation to spacebased laser warning system. The sunlight reflected by earth is the main imaging background light of system′s near infrared detector, and the maximum energy density of reflected sunlight exposuring the CCD is 0.97 mJ/cm2. In the reflected sunlight background, the SNR of attack laser image exceeds 103, for the beacon laser is always below 1. While the reflected sunlight has no effect on attack laser detection, but it is strong background interference to the beacon laser detection. The sunlight direct exposure detector is unavoidable to the warning system. As the maximum energy density of the sun imaging spot is about 20 W/cm2, it will lead to the pixel of CCD saturation or even damaged. Since the imaging spot of sun is similar to the laser, direct sunlight will cause serious false alarm.