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The flowering time plays an important role in the mating opportunities of male and female functions and final reproductive success in plants. The mating environment hypothesis predicts that the differences of flowering time in protandrous species can change individual's phenotypic gender and the mating environment within a population, finally affect the optimal allocation of resources to sexual functions. To determine the effect of flowering time on sexual durations and phenotypic gender in protandrous plants, we recorded the male and female phase durations of all flowers in protandrous Aconitum gymnandrum (Ranunculaceae), and examined the relationships of flowering phenology and floral sexual durations and phenotypic gender. The results showed that the late flowers (top) had longer male duration versus female duration compared to early those (basal) within a inflorescence, showing temporally male-biased allocation. The relatively temporal allocations to both sexual durations also presented a similar trend among plants with different flowering time. Relatively longer male duration vs. female duration in the later flowers or late-flowering individuals, showed temporally male-biased allocation. Furthermore, individual's variation in flowering time affected floral sex ratio within population and the dynamics of phenotypic gender of individuals. It showed a shift from male-biased to female-biased gender during flowering season in A. gymnandrum population, because most of the individuals had only male-phase flowers at the beginning of flowering stage and only female- phase flowers at the end. Therefore, mean phenotypic gender of individuals shifted from femaleness to maleness with flowering time. Our results support the mating environment hypothesis, i.e. male-biased floral sexual ratio (mating environment) early in protandrous A. gymnandrum population leads to female-biased phenotypic gender of individuals flowered early and thus female-biased temporal sex allocation in early-flowering individuals and early flowers within inflorescences in comparison with the late-flowering individuals and late flowers.