A method for forming a semiconductor structure includes sequentially providing a semiconductor substrate having NFET regions and NFET regions; forming an insulation layer on the semiconductor substrate; forming a sacrificial layer on the insulation layer; forming first trenches in the PFET regions, and second trenches in the NFET regions; forming a third trench on the bottom of each of the first trenches and the second trenches; forming a first buffer layer in each of the first trenches and the second trenches by filling the third trenches; forming a first semiconductor layer on each of the first buffer layers in the first trenches and the second teaches; removing the first semiconductor layers in the second trenches; forming a second buffer layer with a top surface lower than the insolation layer in each of second trenches; and forming a second semiconductor layer on each of the second buffer layers.