Goal setting difficulty has been shown to contribute to athletic performance (Burton et al., 2000). However, the potential mediating mechanism of goal difficulty on performance is unclear. Therefore, the purpose of this study was to verify the effect of goal setting difficulty on serving success in table tennis, and determine if self-regulation is the mediating variable. The current study used serving success within a one minute period as the task, and the "Athlete's Self-regulation in Motor Learning" as the measurement tool. The experiment was designed as a 3 (serving frequency: 20/min, 23/min, and 26/min) x 2 (serving placement: left "small triangle", and right "small triangle") model. Participants (N = 60) in the current study were students from a physical education school. These participants were randomly assigned into the experimental and control groups. After the intervention, differences in self-regulation (p < 0.001) and serving success (p < 0.05) between the experimental and control groups were significant. For the experimental groups, there was a significant difference in self-regulation (p < 0.001) and serving success (p < 0.05) before and after the experiment. Serving frequency had a main effect on self-regulation (F (5, 24) = 12.398, p < 0.01) and serving success (F (5, 24) = 37.601, p < 0.001). Moderately difficult goal setting contributed to athletic performance. Regression analysis using bootstrapping methods revealed that self-regulation partially mediated the relationship between the two.