Abstract: Given the material composition and value composition of the total social products of two departments in any given period, there is a unique equilibrium accumulation curve and a unique sustainable equilibrium accumulation rate. Each point on the equilibrium accumulation curve represents a pair of equilibrium accumulation rates of two departments, which can ensure that the supply and demand of total social products reach equilibrium in this period. The sustainable equilibrium accumulation rate can ensure that the supply and demand of the total social products are balanced not only in this period but also in the next period and thus in all subsequent periods. The sustainable equilibrium accumulation rate divides the willingness accumulation rate of all into two parts: convergence and divergence. Under the conditions of decentralized decision-making of capitalist private ownership and pure market economy, the fall in the accumulation rate of willingness in the divergent part will eventually lead to the relative surplus of means of production and economic crisis. While government intervention can partially overcome the shortcomings of decentralized decision-making in a purely market economy, it is still impossible to completely avoid the consequences of the relatively diminishing demand of working people with the capacity to pay and the anarchy of social production as a whole.