Abstract: How environmental factors affect microwave radiation observation was analyzed. Based on the analysis， outdoor experiments were carried out with rock test machine， microwave radiometer， acoustic emission instrument， temperature tester and other equipment to observe microwave radiation characteristics of elastically deformed rock with cyclic loading under cold sky background. Results indicate that the microwave radiation energy changes generated from deformed rock can be detected reliably under cold sky background. In the elastically deformed granite， the microwave radiation energy changes and stress present the positive correlation， with the correlation coefficient of 0.94. The temperature change of the rock surface is positively correlated with the stress too， but the temperature change lags behind the stress change， and the microwave brightness temperature increment is much larger than the surface temperature rise per unit stress. It is verified that the changes in the internal stress state of rock can be detected by microwave observation.

Key words: remote sensing rock mechanics, microwave brightness temperature, cold sky background, rock disaster, stress change, remote sensing monitoring