Forest soils contribute substantially to the global methane uptake. However, compared with the cold and temperate zones, measurements of methane flux from the soils in the tropical forests are still sparse, especially in Southeastern Asia. This gap limits our understanding of the relationship between the methane flux from the soils and the environmental factors, which leads to large uncertainty in the estimation of the methane uptake flux from the tropical forest soils. This study was conducted in Diaoluoshan National Forest Reserve in Hainan Province, China. We measured monthly methane flux from the tropical forest soils by near-infrared laser greenhouse analyzers from September 2016 to September 2018. Soil moisture and soil temperature were measured simultaneously by Decagon 5 TM sensors. Furthermore, we analyzed the relationship between the methane flux with the environmental factors. The results revealed that the soils of the study area served as the sink of atmospheric methane during a 2-year period. The methane uptake in tropical forest soils at the top of the mountain was 0.95 kg CH₄-C hm^-2 a^-1, while that in tropical forest soils at the foot of the mountain was 1.93 kg CH₄-C hm^-2 a^-1. The methane uptake flux in the dry season (from November to April next year) was significantly higher than that in the wet season (from May to October). The former one accounted for about 68% of the methane uptake flux of the whole year. The mean annual soil moisture at the top of the mountain was 19.2% with an intra-annual variance of 2.8%. And the mean annual soil moisture at the foot of the mountain was 12.7% with a bigger intra-annual variance (5.4%) than that at the top of the mountain. Soil moisture acted as the significant predictor of the methane uptake flux and accounted for 76% of the variance. There was no significant correlation between methane uptake flux and soil temperature. For soil moisture lower than 20% (v/v), the relation between soil moisture and methane flux was best fitted with linear regression. For soil moisture higher than 20% (v/v), the tropical forest soils of the study area turned from the sink to the source of the methane flux. According to the relationship between soil moisture and methane flux in the tropical forests, we estimated the annual methane uptake of the tropical forest soils was 1.72 Tg CH₄-C/a. Our results have important implications for long-term methane flux measurements in Southeastern Asia and the estimation of the magnitude of the methane uptake from tropical forest soils.