The InyGa1-y As/GaAs superlattice with an InxGa1-x As (xyGA1-yAs interface was narrower than that at the InyGa1-y As/GaAs interface; in InyGa1-yAs alloy layer, the composition near the GaAs/InyGa1-y As interface was larger than that near the other interface. For the first time, we have explained the composition profile in these kinds of superlattices based on the indium segregation theory. In addition, a new strain relaxation model was presented to explain the differences in the smoothness between the two interfaces.