While many factors have influences on financial institutions' loan pricing behavior, the decision of loan interest rate is one of the most essential. However, current researches often ignore decisive factors of loan rate and their models fail to reflect them. At the same time, the classical Interest Theory fully developed by the 1960s has solved the key problem about the determinations of interest rates, and therefore it has great value to the loan pricing research. This paper reviews the main doctrines of the classical Interest Theory that relates to the decision making of interest rate and the debates caused by them, and then shows some fundamental thoughts contained in the theory that are required for loan pricing study such as risks and benefits of loan projects, capital structure of banks, market basic interest rate and loan maturity.