The masking paradigm is the most used method for generating subliminal stimuli. When both the target stimulus and the mask stimulus are composed of spatial pattern, the mask reduces the visibility of the target. It was called pattern masking effect. Japanese kanji as special visual semantic information, especially when kanji as a subliminal visual stimulus, it is not clear whether Kanji is regulated by the pattern masking effect. Therefore, in this study, we measured the sensitivity index of Kanji detection or discrimination in the masking paradigm using the calculation method of SDT (Signal Detection Theory). By this way, present study investigated the intensity of the masking effect. Results suggested that the sensitivity index of Kanji have the significant difference between the different target presentation time both of detection and discrimination task. As the presentation time is longer, the sensitivity index increases. Results also showed that there is a difference in the cognitive process between detection and discrimination of stimuli, and even if the stimuli can be detected, they may not be discriminated. In addition, as the intensity of the stimulus increased, the intensity of the masking effect became weaker, and it was found that the pattern mask also produces a masking effect in the detection and discrimination of Kanji. According to the research on human visual processing characteristics, it is hoped to help improve the efficiency of computer vision recognition technology.