The characteristics of the human visual system (HVS) are the basis for image technology of display, processing and understanding, and the contrast sensitivity function (CSF) is one of important and special characteristics of HVS. CSF data under the computer display environment has practical applications to the image technologies. Luminance CSF was measured for square-wave patterns on a CRT display, and a psychophysical method for determination of contrast threshold “multi-contrast interactive threshold determination (MITD)” was presented and adopted. Measurements were done for three mean luminances of 10 cd/m2, 60 cd/m2, 90 cd/m2 and eleven spatial frequencies of 0.41 cpd, 0.82 cpd, 1.23 cpd, 1.97 cpd, 3.08 cpd, 3.79 cpd, 4.93 cpd, 7.04 cpd, 9.86 cpd, 16.43 cpd, 24.64 cpd. Measurement results were compared with previous ones that had been measured with the optical apparatus.