Cloud mask is the most important step in studying the effect of clouds on the climate system with satellite data. In order to identify AIRS cloud mask with MODIS cloud mask products objectively, the Nagle's common space matching algorithm is adopted on the basis of scanning geometric characteristics. It is a practical application to combine highspatial resolution products with highspectral resolution detecting images. The key steps for synergistic use of imager and sounder radiance measurements are the collocation in space and time and the determination of the cloud mask products within the sensor's pixel. With the combined MODISAIRS data, the determination can be made of not only AIRS cloud mask, but also cloud phase, effective cloud amount, cloud optical thickness, etc.