Based on field investigation, sample collection and determination of biomass in various organs, we studied the biomass distribution characteristics of reproductive twigs of Dodonaea viscosa in the dryhot valley of Jinsha River. The results showed that: (1) female plants in D. viscosa population in the dryhot valley of Jinsha River had significant advantages, and the sex ratio of male/female was 0.11, which showed a very significant deviation from the ratio of 1∶1 (P<0.001). (2) The morphological characteristics and biomass allocation traits of the twigs were genderdifferent. The flower biomass and total biomass of female reproductive twigs were significantly higher than those of male and bisexual twigs (P<0.05), but there was no significant difference for biomass distribution between male and bisexual. Gender differences have been found in reproductive distribution, but not in leaves biomass of reproductive twigs. (3) There was a significant positive correlation between reproductive biomass of twigs and flower biomass, as well as vegetative biomass and flower biomass (P<0.001), but there was no significant correlation between reproductive allocation and the size of reproductive twigs. Our results indicated that there was no tradeoff between vegetative growth and reproductive growth, and reproductive allocation was not dependent on individual size. This biomass allocation model of D. viscosa might be an adaptation to the special environment of the dryhot valley of Jinsha River.