The infrared laser atmospheric transmittance measurement methods have the problems of high cost and low realtime performance. To address these problems, a method making use of the measurements of sunlight modulation sunphotometer to obtain the atmospheric transmittance of infrared laser is proposed. It is mainly based on measurements and research of analysis on analogy calculation. This method has the advantages of low cost, simple operation, and realtime performance. The infrared sunlight modulation sunphotometer can measure the atmospheric transmittance in wide band. Then, the relationship between the broadband transmittance and the narrowband transmittance can be revised. Finally, the applicable nearmid infrared multiband laser atmospheric transmittance can be obtained. The actual measurement results and comparison experiments are carried out. Compared with the near infrared sunphotometer developed by the laboratory, experimental results show that the statistical error is less than 4%. Compared with POM02, the statistical error is less than 6%. The realtime results obtained by infrared sunlight modulation sunphotometer can be used not only in the correction of laser atmospheric transmission, but also in the evaluation of laser communication and laser transmission.