Using the relative power spectrum method to deal with thermal infrared brightness temperature data of the Fengyun satellite, it is found that there is obvious precursory anomaly before occurrence of the Jinghe M_S6.6 earthquake. The characteristic of abnormal temporal and spatial evolution is that high-value aggregation of the brightness temperature power spectrum appears in the middle, east of northern Tianshan seismic belt and the middle of Altai earthquake belt on July 12, 2017, and then the amplitude and area increases gradually, reaches its maximum on the July 27th, then gradually weakens and returns to normal on August 14th, 2017. The anomaly lasts nearly 1 month. The Jinghe M_S6.6 earthquake occurred at the edge of the anomaly area on August 9th. The average power spectrum time series of the Jinghe M_S6.6 epicentral region are similar to the temporal evolution of the anomaly region. The earthquake occurred when the process of the average relative power spectral value restored from the maximum value to the normal background.