Based on the infrared radiative transfer calculations for 446183 atmospheric profiles, the downward longwave radiation flux at surface and channel brightness temperatures for the FY-4 Imager were simulated. From a regression analysis of the simulated data, a retrieval model relating the flux with channel temperatures and atmospheric precipitable water was established. The model was then applied to Meteosat-8 SEVIRI (Spring Enhanced Visible and Infared Imager) data, adopted as a proxy of the FY-4 Imager, and the downward longwave flux was estimated over an area of (45°S-45°N, 45°W-45°E), at 0000 UTC, 0600 UTC, 1200 UTC, and 1800 UTC Aug 1 2006. The fluxes were then compared with those calculated using empirical equations on ECMWF data. The RMS errors were 12.1, 13.0, 20.7, 12.5 W/m2, respectively. Compared with the RMS 13.7 W/m2 value from GOES-R, the estimates from the model developed in this study would satisfy future climate research requirements.%通过红外辐射传输模拟，计算了446183条全球晴空大气廓线的地表下行长波辐射通量以及FY-4成像仪通道亮温，应用统计回归分析模拟结果，建立了通道亮温与低层大气有效辐射温度的回归关系、大气柱总可降水量与低层大气比辐射率的回归关系，依据黑体辐射定律建立了由卫星观测估算地表下行长波辐射通量的反演模式。初步地，模式应用于FY-4成像仪代理资料Meteosat-8卫星的SEVIRI（Spring Enhanced Visible and Infared Imager）仪器观测数据，估算了2006年8月1日00：00（协调世界时，下同）、06：00、12：00、18：00地理范围在（45°S～45°N，45°W～45°E）的地表下行长波辐射通量，结果与用ECMWF 6 h预报场资料经验计算的通量相比，系统均方根误差（RMS）依次为12.1、13.0、20.7、12.5 W/m2，相关系数分别为0.9256、0.9291、0.9042、0.9325，相比于GOES-R同类产品（RMS=13.7 W/m2），这一直接把卫星通道亮温与低层大气温度相联系的反演模式，其精度性能达到了应用研究对其反演产品的质量要求。
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