Previous study revealed that emotion can be modulated by subjective speed of time. People evaluate experiences more favorably when they think time passed more quickly. However, the intensity of emotion was weak in the previous study. It is not clear whether the subjective speed of time could modulate extremely pleasant and unpleasant emotions, and whether this effect is specific for emotional valence. The present study focused on the effect of subjective time speed on different dimensions (valence and arousal) and levels of emotion. Thirty four right-handed undergraduates (10 male) were paid for participation in the experiment. They were asked to set aside all possible distractions, including watches and mobile phones, thus leaving no external time cues. 200 emotion pictures were randomly chosen from the native Chinese Affective Picture System (CAPS). Emotional pictures and timer were displayed on a screen of a computer running MATLAB with Psychtoolbox. The valence and arousal of emotional pictures were rated with 9-point Likert scale under time flying and time dragging conditions. The timer was 1.5 times of normal in the time flying condition, and it was 0.7 times of normal in the time dragging condition. Participants were told that the task was irrelevant with timer, and he just need to view the pictures and rate the valence or arousal according to his subjective feeling. The valence and arousal of emotional pictures were analyzed respectively. 200 pictures were divided into 10 levels based on their valence scores in the CAPS. The two-way repeated measures analysis of variance (ANOVA) was conducted on valence with subjective time speed (time flying & time dragging) and valence levels (10 levels) as within-subject factors. The repeated ANOVA revealed a significant interaction between subjective time speed and valence levels. The sample effects tests revealed that there were no significant differences between time flying and time dragging conditions in the four low levels of valence (from level 1 to level 4), whereas the scores of valence were significant higher in the timing flying than time dragging in the six high levels of valence (from level 5 to level 10). Then 200 pictures were divided into 10 levels based on their arousal scores in the CAPS. The repeated ANOVA on arousal did not reveal any significant main effect and interaction. The present study confirmed previous finding that emotion can be modulated by subjective speed of time. Furthermore, our results showed that the valence evaluation of neutral and positive pictures was more positive under time flying compared with time dragging, whereas the subjective speed of time did not modulate the valence evaluation of negative pictures as well as the arousal evaluation of all pictures. The results suggest that the "You’re having fun, When time flies" effect is valence-specific.