Abstract: The plot ratio is an important index of urban land development intensity, how to estimate the plot ratio quickly and accurately has been a hot issue. Building height is the base of extracting the plot ratio, according to traditional height extracting based on the shadow, introduced a height correct model and improved the calculation accuracy effectively. Based on ZY-3 image, extracted the shadow features by using object-oriented technology, calculated the building height through the height correct model, got the floor number and extracted the plot ratio combined with the area of the buildings and residential district. Finally, the validating result based on the floor number shows that the accuracy of estimating floor-number has increased from 90.213% to 92.375% after the height correct model, which has demonstrated the validity and necessity of this model and the prospecting applications of ZY-3 image in extracting the plot ratio.