There are over 20 years' research experience for remote sensing used in crop monitoring in North America, European counties and China. A crop monitoring system using remote sensing has been developed and used by China Ministry of Agriculture. As China is a large country with complicated landscape, multi-crop systems and small family farms and the government needs operational system at a national scale, many key techniques still need researching. The main issues discussed in this paper include remote sensing data processing, crop discrimination, crop area measurement, crop condition assessment, disaster monitoring, yield estimation, and operational system development. Based on the authors' experience, the progress, problems and the main ideas for solutions of the operational system development at a national scale are discussed in this paper.