Abstract: The research subject of Marx's Das Kapital includes the exchange relation of the market. It is a classic theoretical economic masterpiece on the mode of production and the destiney of the market. Theory of socialist market economy needs a deeper understanding on Marx's fundamental theory on market economy and highlighting the fact that Das Kapital is essentially a theoretical work on market economy is the precondition. Therefore, based on the context of Das Kapital, pointing out that the fundamental principle of Marx's economic theory is also the fundamental theory of market economy, is helpful to re-understanding the vaule of Marx's theory from the market economics side and provide important theoretical foundation of China's theoretical economics.