In order to clear the relationships between photosynthesis and leaf N, leaf P, SLA of tropical trees and test the differences of relationships among life-form groups (tree, shrub-like tree and shrub), seedling and saplings of 101 species in tropical montane rain forest located in Diaoluo Mountain of Hainan Island were selected. The net photosynthesis based on area and mass (Aarea and Amass), leaf nitrogen content based on area and mass (Narea and Nmass), leaf phosphorus content based on area and mass (Parea and Pmass) and specific leaf area (SLA) were measured and calculated. The results showed that Aarea and Amass tended to be of shrub>tree>shrub-like tree. The one-way ANOVA showed that Aarea between shrub and shrub-like trees was significantly different (p<0.05), and for Amass, there were significant differences between shrub and shrub-like trees, and shrub and tree species (p<0.05). The relationships between Aarea and Nmass were most significant in all three life form groups and for all species (p<0.0001); the correlation between Aarea and Pmass was most significant in shrubs (p=0.0038), shrub-like trees (p=0.0002) and for all species (p<0.0001), but not significant in trees (p>005); The relationship between Aarea and SLA was most significant in shrubs (p=0.0006), trees (p<0.0001) and for all species (p<0.0001), however not significant in shrub-like trees (p>0.05). The relationships between Amass and leaf N, SLA were most significant in all three life form groups and for all species (p<0.0001); on Amass vs. leaf P, there were significant correlations in tree group (p=0.0377) and most significant correlation in shrub group (p=0.0004), shrub-like tree group (p=0.0018) and for all species (p<0.0001). Stepwise regression showed that the predicted Amass values were closer to the observed values than the predicted Aarea values. Thus, it could be concluded that the relationships got from seedling and sapling measurement is close to those from mature individuals; the correlations between photosynthesis and the traits of Nmass, Pmass and SLA are significant, and the relationships are stronger and more stable for Amass than for Aarea.