Setting or calibrating gamma value is a simple and practical method for controlling color on computer displays. The accuracy of visual estimating gamma value of CRT displays is investigated by using the stripe photometry method. The investigated factors include stability for one subject, consistency for different subjects, influence of stripe with different luminance levels. The estimated results were compared with ones measured by instruments. The experiments were conducted on hp 21″ CRT display. The results show that the same operator’s matching result is very stable and matching values vary little for different subjects, gamma mean values by visual estimation for R, G, B and luminance channels are 2.18, 2.17, 2.40, 2.20, and the measured values are 2.13, 2.05, 2.37, 2.09 respectively. The difference between estimated and measured gamma values is about 0.08. Appropriate choice of stripe with different luminance levels will make visual matching more easily, and the estimated gamma value is more adjacent to the measured value.