This paper constructs a portfolio choice model to depict the portfolio selection decisions in fixed investments and financial investments made by real sector firms under financing constraints． The theoretical model shows that the relative risk of fixed investment，the difference between the adjusted rate of return of financial assets and the interest rate on liabilities，the difference between the adjusted rate of return of fixed assets and the interest rate on liabilities all affect the portfolio choice decisions of firms with financing constraints． The former two factors promote the financial investment，while the third one suppresses the financial investment． The influence of the second factor is larger than the third one． Moreover，the difference between the rate of return on financial assets and the rate of interest on liabilities has a greater impact than the difference between the rate of return on fixed assets and the rate of interest on liabilities． The paper uses firm-level panel data of non-listed real sector firms from 1998 to 2009 for the empirical research，and finds that the influencing factors of the financial assets’ratio in the portfolio of non-listed real sector firms are consistent with the factors proposed by the theoretical model． Through the theoretical model and the empirical results，this paper shows that the rise of the rate of return on financial assets can promote the financialization of financial-con-strained firms to a greater extent than the decline of the rate of return on fixed assets．