In this paper,a new method of accurate calculation of the polarizatio n ratio (PR) and the fabrication of linearly polarized blue LED based on nanoimprint lithography of A l grating are proposed.Taking the lambertian emission pattern of LED into consi deration,the PR ratio is calculated as the ratio of t he light intensity of the transmitted TM mode to that of the transmitted TE and TM modes through the grating within the half- plane incident angle.Based on this method,the effects of the factors,such as the grating material,grating period,fill factor,grating height,on the PR ratio are analyzed.The results show that by using Al grating,the PR ratio is almost equal to 1,when the grating period, fill factor and height are 150mm,0.5and 120nm,respectively.In addition,the i nductively coupled plasma etching of the Al grating is optimized.The experiment results indicate that the polarization extinction ratio(PER) of bl ue LED is substantially increased from 1.0∶1to 2.2∶1.0.