Abstract: Abstract: Recently, there is a growing global concern over food loss and waste and its impacts on resources and environment, especially in the developing countries. And it is estimated that about one third of food output worldwide was lost and wasted each year, which has been consistently recognized to be another threat to global and regional food security. Therefore, in addition to maximizing crop yields to enhance food security, reducing food loss and waste from food system is considered as another key strategy to combat hunger and sustainably provide food for the world. However, knowledge about food loss and waste is entirely inadequate worldwide, especially in developing countries including China. Therefore, it is urgent to conduct researches on food loss and waste in different regions in order to comprehensively evaluate global food security situation. In this research, based on the researches available and the data collected from CNKI (China National Knowledge Infrastructure) and other literature database, a method was built and developed to quantify crop postharvest losses, despite the uncertainties due to data limitation. Rice, wheat and maize were chosen as the major crops to be analyzed. Crop postharvest segment was divided into 4 sections, including crop harvest, transport, drying and storage, and each section had different loss ways or loss based on different technology or from agricultural machine, in which crop harvest was divided into combine harvesting and two-stage harvesting, transport was divided into package and bulk transporting, drying was divided into air and mechanical drying, and storage was divided into household and depot storage, and correspondingly the data were classified. With the method presented in this research, a comparative analysis of postharvest losses from the major crops in China was carried out. The results showed that there was a much higher total crop postharvest loss (CPHL) ratio in China compared with the developed countries, the CPHL ratios were 6.9% for rice, 7.8% for wheat and 9.0% for maize, respectively, and the total average CPHL value was 7.9%. Moreover, for the CPHL ratio, the section of crop storage had the largest contribution compared with other sections of crop postharvest segment, and the proportion reached 40.3% in the total crop losses. The second was from the section of crop harvest, with the proportion achieving to 31.4%, and the sections from crop transport and drying had the minimum losses, which were 11.1% and 17.2%, respectively. In addition, household grain storage and crop two-stage harvesting were the most serious loss ways. And based on the different scenarios of crop loss reduction, an evaluation was performed for the year of 2010. The different scenarios indicated that by improving agricultural technical conditions from different sections of crop postharvest, the CPHL ratio could be effectively reduced, and the optimal scenario could cut down CPHL ratio to be less than 4%. So, there is a large CPHL reduction potential existing in Chinese crop postharvest sections. However, to achieve the CPHL reduction, the policies of agricultural science and technology made by the Chinese government, have to play an important role in the comprehensive measures such as raising farmers' consciousness of scientific grain storage, promoting mechanization levels of crop harvest and improving crop harvest quality.