Sex ratio is one of the important factors affecting insects longevity and fecundity. In this experiment, the females and males of Bactrocera cucurbitae(Coquillett) were paired according to five sex ratio combinations (1∶11, 2∶10, 6∶6, 10∶2, 11∶1). The effects of different sex ratios on the mating and reproduction of B. cucurbitae were studied by observing the biological parameters such as the average eggs per female, hatching rate, oviposition duration, and longevity of males and females. The results showed that the mating times of males and females were significantly affected by sex ratio. As the proportion of females increased, the average mating times of females decreased significantly, whereas that of males showed an increasing trend. The average mating times of male with the sex ratio of 11∶1 was the highest, which was 10.8 times. In addition, the sex ratio had no significant effect on the average number of eggs laid per female or oviposition duration, but significantly influenced the hatching rate. Both female-biased and male-biased sex ratios were not conducive to the hatching rate. When the sex ratio was 6∶6, the hatching rate was the highest, which was 74.6% ± 1.6%. Sex ratio did not affect female longevity significantly but affected male longevity significantly. With the increase of female proportion, male longevity decreased. Sex ratio has certain effects on the mating ability and reproductive fitness of adults. The above results provide a scientific basis for further research on green integrated pest management strategies for B. cucurbitae.