The purposes of this study were to explore the influences of different goal difficulity (difficult, easy, none), task difficulity (difficult, easy) and feedback type (positive, none) on elementary school student's volleyball serving performance, intrinsic motivation and their interactions. Subjects involved were 144 6th grade elementary school students which came from four different classes on the same campus (male78, female66, mean age=12.67 years), and each class was assigned randomly to different task and feedback type situations. Students in each class were divided into three different goal difficulity sets. This experiment was 2 × 2 × 3 designed and a Volleyball-Serving-Intrinsic-Motivation Inventory developed by the researcher was administered. Three-way ANOVA and post hoc comparison were utilized for data analysis. The results showed: in the aspect of volleyball serving performance, only the main effect goal difficulity was significant; in the aspect of intrinsic motivation, the interactions of task difficulity with feedback type, task difficulity with feedback type with goal difficulity were significant, respectively. Not only this study verified Locke's theory, but also offered some suggestions to both further related studies and researching directions.