According to the theory of integration of multi-resource data， we refer to the demographic data of Yunnan Province released in 2011 after the Sixth National Population Census，to set the residential area as an indicator of population distribution in Yunnan． Then by using GIS to analyze the relation between the population distribution and the factors such as landform，topographic slope，amplitude of landform relief，and land-use，we get the weighing coefficient of the impact factor of population． Finally，we use the unified model of population and area to estimate the earthquake-affected population by way of kilometer-grid transformation and check the precision of the result． To test the practicability of our estimation，we calculate with various methods the population of the disaster area of the Eryuan，Yunnan，M5. 5 earthquake on March 3，2013． By comparing the results from these methods，we find that the estimated population through the kilometer-grid transformation is highly-related with the real population; the correlation coefficient is over 0. 89． So， the estimated population is reliable for the quick judgment of the disaster condition．