In order to study our country's monetary policy, we try to set up a general equilibrium model for a bank's credit behaviors, an enterprise's investment behaviors and residents' consumption behaviors.We demonstrate in theory that, on condition of general equilibrium, a market structure of bank monopoly is disadvantageous to the increase of credit supply; the domestic consumption demand is away from sufficiency because the income effect of reducing interest rates is greater than the substitution effect; an expected inflationary or deflationary situation is not helpful to reduce or increase credit supply and credit demand.So the effect of our monetary policy has been and will be inefficient.