Abstract: As an important variable,expectation price affects the behaviors of consumer and producer in micro-market.Expectation price of producer contains not only the past expectation price and real price but also the past supply and demand.Price changes with the relation of supply and demand.Under certain scopes,the intrinsic adjustment mechanism(invisible hand) may demand price.But price has no longer the stability if it goes beyond the scope and the market ineffectiveness may take place.

Key words: disequilibrium, expectation price, excess demand, stability