MODIS V4 fire detection algorithm has problems of fire omissions at large scan geometries.In order to solve this problem, the brightness temperature changes of fire pixels, which consist of fire and background surface at different scan geometries, were analyzed. Active potential fire detecting thresholds were developed according to scan geometries.A fire detection algorithm for the HJ-1B-IRS based on MODIS V4 algorithm was presented. Using HJ-1B-CCD data, we validated the fire detection results of HJ-1B-IRS with the fire detection method based on smoke plumes. In comparison to MODIS fire products, HJ-1B-IRS fire product shows advantage on fire location and small fire detection.