Although there were controversies on whether terrestrial plants emit methane (CH₄) under aerobic conditions, more and more researches confirmed that plants themselves did emit CH4, and sunlight was one of the important factors which effected the CH₄ emissions from plants. In this study, we used stable carbon isotope-labelling technique combining with potted experiments to discussed the source of methane emitted in situ from Castanopsis carlesii and Cunninghamia lanceolata and their responses to sunlight and shadowing. The results showed that there were significant differences in the stable carbon isotopic value of labeled and unlabeled leaves between Castanopsis carlesii and Cunninghamia lanceolata, the stable carbon isotopic value (δ¹³C)of the labeled Castanopsis carlesii and Cunninghamia lanceolata leaves was 128.9.and 71.1 times higher than that of the unlabeled ones. Similarly, there were significant differences in the stable carbon isotopic value of methane from the labeled branch leaves of Castanopsis carlesii and Cunninghamia lanceolata and that from the unlabeled ones. Been sealed 2 hours, the stable carbon isotopic value of methane (δ¹³CH₄) isotopic signatures of methane, which emitted from Castanopsis carlesii and Cunninghamia lanceolata were 21.1 and 28.2 times higher than that of the unlabeled ones. These results indicated that the most detected CH₄ emission during our experiments were from plants themselves. Shadowing and natural lighting experiments showed that the CH₄ emission rate of Cunninghamia lanceolata was 29% higher than Castanopsis carlesii under sunlight, the mean CH₄ emission rates of them were 6.3 and 4.88 ng CH₄·g^-1DW·h^-1, respectively. The fluctuation rule of CH₄ emission rates are similar between the two species under sunlight, both of them were reduced at first, and then increased, finally, they were reduced again. However, the rule was different under shadowing, the mean CH₄ emission rate of Cunninghamia lanceolata was 23% lower than under sunlight, especially after 15 days, the CH₄ emission rate reduced significantly, until June 30^th, it was only 15.1% of that detected under sunlight. The mean CH₄ emission rate of Castanopsis carlesii were not significantly different under sunlight and shadowing, they were 6.3 and 5.67ng CH₄·g^-1DW·h^-1, respectively; but after 5 days, the CH₄ emission rate was 71% higher than under sunlight, it reached up to 10.45 ng CH₄·g^-1DW·h^-1, then it dropped sharply, and obviously lower than under sunlight, until June 30^th, it was only 43.1% of that detected under sunlight. These results suggested that sunlight promoted methane emission rate from plants.