Abstract: Minolta chlorophyll meter(SPAD-502) was a compact portable lightweight meter that was used in the nitrogen fertilizer recommendation in recent years in developed countries.The principle of the meter underlay was the different absorbance characteristics chlorophyll on the red region and infrared region.Then the content of chlorophyll in plant leaf could be detected by the amount of light transmitted by leaf in the two wavelength regions.This instrument could be a very useful tool for plant N status diagnosis in crop production due to its convenient,rapid and precise reading.In order to make use of chlorophyll meter in crop N recommendation,it is necessary to make clear the relationship of the SPAD reading with leaf N content and crop yield of different crops under field management measures to elucidate the diagnosing position and leaf sampling and set up the critical values for N recommendation in practice.The physiology basis used by SPAD-502 chlorophyll meter to determine the crop nitrogen status was introduced in this paper.The relationship of SPAD readings and nitrogen content for different crops,critical chlorophyll value at different growth stage,leaf position for testing and necessary numbers for sampling were also reviewed.Some factors such as crop,environmental condition and crop management measures which influencing the readings of chlorophyll meter was discussed in this paper.