Abstract: The present invention provides a protein fragment for fusion expression of ion channel protein and transport protein. The protein fragment is a Bril protein fragment or a T4L protein fragment. Also provided is a method for preparing a fusion protein by inserting a Brit protein fragment or T4L protein fragment into the N-terminal, C-terminal or intramembrane loop region of the ion channel protein and transport protein so as to improve its, in-vitro stability and crystallizability.