On the basis of an observation to summer maize canopy PAR during growing period at Luancheng,Hebei,the incident PAR,the reflective PAR of the canopy,the PAR reached the land surface through canopy,the reflective PAR of the land surface,the reflectance of land surface,the Absorbed Photosynthetically Active Radiation(APAR)and the reflectance diurnal change of the canopy and land surface under clear and cloudy conditions respectively were stud-ied in this paper.Also,the FPAR at an interval of five minutes and the average value of a day were calculated according to each PAR components in canopy.Then the relationship between daily variation of FPAR and crop growth periods as well as the variation of LAI were examined and a linear relationship between FPAR and LAI was presented.