Marx s theory of "the equality of profits and the law of average rate of profit" is of universal significance, especially to the current reform of industrial structure in China.

The theory of average rate of profit raised by Marx is scientific and systemic.

This paper sums up and analyzes some doubts on Marx’s theory of average profit rate, probes into the reasons why these doubts exist, and expounds how to understand correctly this theory.

Marx s theory of average profit rate : the average profit rate is the requirement of social productivity and market economy,and the average profit rate is always realized by way of the capital flow,so the capital flow is essential not only for the realization of average profit rate,but also of the optimizations of industry structure and of resources.

Sector average profit to investment rate and profit-tax to investment rate are two of the main references to investors on selection of investment opportunities, and are also the lowest expectation of investors on value of the return to the investment.