Abstract: SPAD-502 meter provides a simple, fast and nondestructive method to monitor rice nitrogen status and predict the need for fertilizer-N topdressing on time, but the precision was influenced by many factors. Because SPAD-502 meter diagnoses the nutrient status indirectly by means of leave color (value of SPAD), it is important to understand factors that affect SPAD readings in order to improve its application purpose. In this paper, factors influenced SPAD readings, such as rice variety, development stage, the leaf position, the point on the leaf and environment were studied. The research progress on improving the precision of rice nitrogen diagnosis by quantifying the relationship of SPAD reading to nitrogen content, as well as nitrogen recommendation by quantifying the relationship of SPAD reading to topdressing were also reviewed. For a purpose of further improving the precision of nitrogen status diagnosed by SPAD-502 meter and fertilizer recommendation, few questions need to be settled was put forward.