[Objectives] Studying the morphological differences between male and female in amphibians not only helps to understand the patterns and mechanisms of sexual dimorphism in species, but also has important implications for the study of their reproductive strategies, reproductive investment, and evolutionary selection pressures. [Methods] In this study, we collected 61 individuals (12 females and 49 males) of Polypedates megacephalus from a permanent pond on the campus of Lishui College in Lishui City, Zhejiang Province, China, from April 2020 to August 2021, and measured 12 morphological characteristics including snout-vent length, head length, mouth width, forelimb length, hindlimb length, and weight to investigate sexual dimorphism in this species. We also collected data on clutch size and hatching success to analyze female reproductive ability. One-way ANOVA was used to test for differences in body weight and snout-vent length, and a one-way ANCOVA test using body length as a covariate to examine whether there were differences in head length, mouth width, mouth length, eye diameter, interocular length, forelimb length, hindlimb length, forearm-fingers length, tibia length, foot length, and internasal length between sexes. If differences were found, we further employed Tukey’s multiple comparison test. We used the Kruskal-Wallis test to investigate whether there were differences in clutch size and hatching rate of P. megacephalus among different breeding months. We also performed a linear regression analysis to examine the linear relationship between maternal body length and clutch size. [Results] Our results showed that P. megacephalus exhibited significant sexual dimorphism, with females larger than males. Except for eye diameter, tibial length, and internasal length, all other morphological characteristics, including snout-vent length, head length, mouth width, mouth length, interocular length, forelimb length, hindlimb length, forearm-fingers length, foot length, and weight, were significantly higher in females than in males (P < 0.05) (Table 1, Fig. 1). The clutch size and hatching success of P. megacephalus females were significantly affected by season, with the highest clutch size occurring in April to May (Table 2) and the highest hatching success occurring in June (Table 2) The number of eggs carried by females was positively correlated with body length (Fig. 2). [Conclusion] Therefore, we speculate that fecundity selection is the main factor causing sexual dimorphism in P. megacephalus, with females increasing their individual size to increase their egg-carrying capacity and improve reproductive output. The reproductive period of P. megacephalus is influenced by season, and it has evolved a pattern of extended reproduction to better adapt to the early or delayed rainy season.