Abstract: In order to reveal the law of gonadal occurrence and development,the fertilized eggs were incubated in the thermostat in soft-shelled turtle,Trionyx sinensis.Hatching medium was coarse: medium: fine sand(volume ratio 1∶4∶1) with the temperature of(3-±0.5)℃ and the humidity of 7%- 8%.The relative humidity was 75%- 80%.The samples were fixed in Bouins' liquid,including embryo of 1- 16d,17d,and then,the gonad of 7d after going out of shell and that of the one,two,three and four-year-old turtles.Fixed samples were embedded in paraffin,sliced and stained with HE.Simultaneously,the embryo proper of 16- 4d after incubation was anatomized and the gonad was measured.Same treatment was applied in female and male turtles of 7d out of shell,one,two,three and four-year-old.Results showed that primordial germ cells moved to the endoderm in the vicinity of the midgut at 7-h after incubation.Genital ridge developed at the 5d,and the gonad differentiated into the cortex and medulla at the 13d.After three days,the gonad began to differentiate and the testis or ovarian formed at the --d.Smooth in the surface,colorless and transparent tremellosely,the gonad was a slim short tubule at embryonic period in young soft shelled turtle and one-year-old turtle.The testis was long-oval at two,three and four-year-old turtles.The sizes of 16d,-0d,-8d and 34d gonad were 0.64 mm×0.2- mm,0.83 mm×0.27 mm,1.00 mm×0.29 mm and 1.21 mm×0.3- mm respectively.The sizes of ovary were(1.37±0.14) mm×(0.51±0.07) mm,(7.60±0.95) mm×(2.94±0.45) mm and(45.9±4.08) mm×(4.10±0.47) mm respectively in the 7d turtle out of shell and one,two-year-old turtle,while those of testis were(1.21±0.16) mm×(0.37±0.05) mm,(12.21±4.25) mm×(3.37±0.70) mm,(25.40±1.00) mm×(9.09±0.20) mm,(27.36±0.85) mm×(10.33±0.14) mm and(38.76±3.36) mm×(15.71±2.00) mm respectively in the 7d turtle out of shell and one,two,three and four-year-old turtles.Oogonial period was observed at the ovarian development in young soft shelled turtle.Seminiferous tubule of testis was not obvious with the spermatogonia in the tubule at oogonial period of ovaries.Primary follicular period was found at the ovarian development in one-year-old turtle,and the number of spermatogonia increased in the seminiferous tubule of testis.The ovary was at the growing follicular period in two and three-year-old turtle,and mature follicular was observed in the ovary at the end of three-year-old turtle.Primary spermatocyte was observed in the seminiferous tubule of two-year-old turtle,and spermatid and sperm occurred in the seminiferous tubule of three-year-old turtle.The ovarian development of four-year-old turtle was at the mature follicular period.Spermatogenous cell,primary spermatocyte,secondary spermatocyte,spermatid and sperm arranged in turn from tube wall to lumen in the seminiferous tubule.The conclusion was that the testis or ovarian formed at the 22d of the embryonic development in Trionyx sinensis at(3-±0.5) ℃,however,the gonadal development and maturity occurred at four-year-old turtle in natural conditions.