This research is based on expectancy-value theory. Through an analysis using dynamic structural equation model, we clarified the dynamic effect of success expectation and interest value on mathematic achievement. We employed empirical sampling to collect intensive longitudinal data from 46 elementary school students. A standardized mathematic achievement test was administered after the course. The analysis revealed an autocorrelation and a cross-lagged effect between success expectation and interest value at the within-person level. At the between-person level, success expectation positively affected mathematic achievement, whereas interest value negatively affected mathematic achievement. However, the random slope related to the cross-lag effect of success expectation positively affected mathematic achievement. On the basis of the study results, suggestions were provided for practical application and future research.