Javelin goby (Synechogobius hasta) is an important part of the coastal fishing of China, Japan and Korea, which has high economic and development value due to its tender meat and delicious taste with abundant protein and polyunsaturated fatty acid. In order to understand the breeding characteristics, the adult S. hasta collected from Haizhou Bay were used as materials to detect the data about sex ratio, fecundity and germ cells for analyzing the gonad feature and law of embryonic development, besides, the effect of main environmental factors on the fertility rate of S. hasta were also assessed by orthogonal experiments in this study. The results showed that sex ratio of S. hasta between the female and male was 1.03∶1.00 in the non-reproductive period and 3.26∶1.00 (P<0.05) in the reproductive period, respectively, which indicated the number of females was significantly more than males in the breeding stage. The individual differences in fecundity of S. hasta were large, with a maximum value of 7.15 times the minimum. The absolute fecundity ranging from 5 987 to 42 828 (19 655±12 551), while the relative fecundity ranging from 42 to 263 (144±59), and significant positive correlation between brood amount and body weight were recorded (R=0.82). In early March, the male fish delivered the spermatophore to the female abdominal cavity before the matures of female fish. A small amount of spawning was observed in mid- March, and a large number of concentrated spawning occurred in early April. The type of goby’s ovium was anisolecithal, and the mature ovium were at the stage of the middle of the second mature division. The mature ovium was light yellow, translucent and agglutinant containing several oil balls with the diameter of (1.53±0.16) × (1.33±0.20) mm. The sperm density was (1.43±0.14)×10⁹ ind/mL, and the average number of sperm produced by each male was (5.43±0.53)×10⁹ ind. Embryonic development process included 7 stages: placental formation, cleavage, blastula, gastrula, neurula, organ formation and hatching, in which the organ formation stage also consisted of body segment stage, optic rudiment stage, capsula opitca stage, tail bud stage, eye crystal stage, muscular contraction effect stage, otolith stage, heartbeat stage and eye pigment deposition period. Under the conditions of incubation water temperature (17±1) ℃, it took 149 h 50 min to hatch, and the required accumulated temperature was 2 455.82 h·℃. The results of orthogonal experiments showed that the highest fertility rate was obtained under the conditions of temperature of 19℃, the salinity of 32, and pH 8.0. The influence of environmental factors was in the following order: salinity>pH>temperature. In conclusion, the female gonad of S. hasta matured later than that of the male fish; the embryo development period was relatively long, and the fertilization rate could be improved by higher water salinity. This study preliminarily clarified the timing characteristics of the embryonic development of S. hasta, enriched the basic data of reproductive biology, and provided theoretical evidence for the artificial breeding and conservation of germplasm resources.