A detailed experiment and a theoretical analysis of two-step ion-exchanged glass optical power splitter are reported. In order to facilitate quantitative analysis, a rational model of physics for a rise inverse sine structure of 1×2 S-branch power splitter in glass is proposed. In thermal ion exchange, the distribution of normalized refractive index of two-step ion-exchanged optical power splitter and the distribution of splitter refractive index of different exchange time have been gotten. On this basis, these surface half-round channel waveguides are fabricated by first performing a thermal Tl+ exchange in melt Tl2SO4 through a mask patterned on the glass surface. The resulting surface channel waveguides are then buried by second thermal Na+ exchange, unmasked ion exchange, in melt NaNO3. In this step the Tl+ ions migrate from the glass, and the wavguides are buried below the glass surface. A optical power splitter of insertion loss 0.15 dB and coupling ratio 50∶50 has been realized.