Previous studies have separately explored the impact of parents' academic support and expectation on students' academic achievement. However, few studies have explored the common impact of these two factors simultaneously and from the perspective of development. The purpose of this study was to explore the dynamic long-term impact of parental academic support on students' happiness and academic achievement, as well as the moderating effect of parental academic expectations. A total of 539 students from a high school in eastern China participated in a five-wave three-year survey with measurements with the interval of half a year. The results showed that the slope of parental academic support across the five measurements predicted the slope of students' academic performance through the slope of student happiness. In addition, the slope of parental academic expectations moderated the effect of the slope of parental academic support on the slope of student happiness. Specifically, this positive effect was significant only when the slope of academic expectation is positive. Theoretical contributions and practical implications are also discussed.