The hypothesis of optimal diversification level is a representative subject in the study of diversification of the corporations, This study employs the Jacquemin - Berry entropy measure of diversification to analyze the DP relationship from a sample of 143 listed corporations of Shanghai and Shenzhen in China. The results of our tests indicate that no significant relationship exists between diversification and performance, Thus, we provide no validated results to support the optimal diversification level of the listed corporations existing in China. But the variation of profitability decreases as the diversification level of the corporations increases, so as to reduce the uncertainty of the profitability.