The influence of the luminance at photopic level on the neural contrast sensitivity function (NCSF) of visual system is studied. The contrast sensitivity function (CSF) of the visual system and the modulation transfer function (MTF) of the eye′s optical system are firstly measured. Then the NCSF is gotten through the calculation method. NCSFs of four individual eyes are respectively determined in the cases of white light (with the luminance of 15, 210 and 310 cd/m2). The results show that, the NCSF of white light mounts up considerably and the curves shift toward higher spatial frequency as the luminance increases. However, the change of NCSF is somehow different from individual to individual. With the increase of luminance, the variation tendency of the CSF is similar to that of the NCSF, while the gain is much larger than that of the NCSF, especially in the region of higher spatial frequency. It is the NCSF, rather than CSF, that reflects the luminance sensitivity in the retina-brain neural system, because the influence of the eye′s optical system is excluded.