A method of floor area ratio extraction is proposed by extraction of construction shadow in high resolution remote sensing images. Image processing is used firstly to extract large range construction shadow in urban building area,then these shadow are vectored and the shadow coordinates are converted to spell image contiguity breadth. Secondly, FAR is calculated based on regress analysis between construction shadow area and construction area by taking into account of construction’s orientation. At last,FAR of Shanghai central city zone is extracted and the results are validated. The result indicates that the method can extract FAR in high resolution satellite image effectively.