Abstract: The recent researches on estimating crop leaf area index(LAI) with remote sensing were mostly concerned about only single type of crop or a region whose crop planting structure is simple. The large scale crop LAI estimating method was used in the research. After analyzing the relationship between observed LAI and NDVI in four representative observing areas in China, LAI estimating models for four representative crop planting structures were built. Country-scale crop LAI estimating model of China was derived for the first time by extrapolating the four models with zonal data of China for different crop planting structures. The crop LAI of China was computed with the model and the result was validated with the observed crop LAI data obtained in 863's integrated experiment for RS in Shandong Province. The results of validation show that max relative error of the model is 39% while the average error of it was 19%, which means the model achieves a high precision. The result of the model has been widely used in "China Crop Watch System with Remote Sensing".