The phenomena of high initial IPO returns and poor long-term returns are popular in China’s stock market，and the traditional rational financial theory is unable to explain such phenomena at the same time． In this paper，based on the behavioral financial theory，from the perspective of investor sentiment and disagreement，we construct a buy-sell imbalance( BSI) index，using initial IPO from the investors’trading data，to represent investor sentiment to study these IPO phenomena in China． We find that investors’sentiment and disagreement both have significant positive impacts on the initial returns，and when the disagreement is big，the impact of sentiment is more serious． Meanwhile，sentiment has significant positive impact on the long-term abnormal return，but disagreement has no such impact． This paper provides explanations to the IPO puzzle in China’s stock market from the perspective of individual investors’irrational biases．