By using the co-integration testing and error correction model (ECM), this paper investigates long-run and short-run linkages between stock exchange index and GDP. Through exploring the data from the Chinese economy, the authors get the evidences that suggest the equilibrium between stock exchange index and GDP has been broken. Then based on Expectations Theory, they reveal the reason of the stock market down-going with the increase of GDP. Then on the light of above analysis, some adviec is given.