Using the fertilized eggs and larva of Strongylocentrotus intermedius, the effects of high temperatures and low salinity on the early embryonic development of the S. intermedius were investigated, and the tolerance of larvae at various stages to temperature and salinity were studied. Central Composite Design and Response Surface Methodology were used to study the interactive effects of temperatures (12–26 ℃) and salinity (22–34) on the early embryonic development processes of S. intermedius, with the aim of establishing a quantitative relationship model of temperature and salinity on the development processes of embryos, and then through statistical optimization methods obtain the best combination of temperature and salinity. The results showed that the early embryonic development time of S. intermedius first shortened and then lengthened with temperature increase. With salinity decreasing, the early embryo development of S. intermedius increased. The linear effect and the quadratic effect of temperature, and the linear effect of salinity on the early embryonic development process of S. intermedius were significant (P<0.05). The absolute value of the linear coefficient of temperature was greater than the linear coefficient of salinity. The combined effect of temperature and salinity on the early embryonic development of S. intermedius was not significant (P>0.05). The model equation of the 2-cell, 8-cell, 16-cell, blastula, float, and four-arm pluteus larvae toward temperature and salinity were established, with the coefficients of determination (R2) being 0.9576, 0.9508, 0.9689, 0.9932, 0.9681, and 0.9763, respectively. At a temperature of 20.47 ℃ and a salinity of 31.46, the development time of the 2-cell, 8-cell, 16-cell, blastula, float, and four-arm pluteus larvae of S. intermedius were the shortest, which were 1.28 h, 2.07 h, 3.31 h, 4.14 h, 11.28 h and 47.31 h, respectively. The results indicated that a high temperature and low salinity will prolong the early embryonic development processes of S. intermedius. The findings provide a theoretical basis for the artificial breeding of S. intermedius.