中文摘要：

借壳上市能使企业快速上市融资，促进产业发展，但借壳上市产生的成本和内幕交易行为却是不容忽视的重要课题。在对4家快递企业借壳上市的分析中发现，壳公司股东通过“卖壳”取得了巨大收益，借壳公司股东虽然获得了上市后的股票增值收益，但成本高昂。信息泄露导致借壳上市存在市场异动，内幕交易提升了公司借壳前的股价，降低了市场流动性，增加了借壳成本。借壳上市市场异动呈现倒U型结构，知情交易者的交易提前，且变得更加隐蔽。政府应采取措施加快注册制改革，完善退市制度，提高公司上市退市的效率，降低壳资源价值，加强信息披露监管，降低公司上市成本，打击内幕交易行为。

英文摘要：

Backdoor listing allows enterprises to quickly be listed and promotes industrial development,but the cost and inside trading are important issues that could not be ignored.Using four express companies as the sample,the authors analyze the change of cost,income,stock price and volume of backdoor listing and carry out study on the impact of backdoor listing on market liquidity.It is found that shareholders of shell companies gained huge profits and the backdoor companies gained high value after listing,but the cost was high.Information disclosure leads to market change and inside trading increases the price,reduces the market liquidity and increases the backdoor cost before listing.The market transaction turns into an inverted U structure,and the informed trader's trading becomes more subtle and ahead of schedule.Government should take measures to speed up reform and delisting system,strictly control backdoor listing,strengthen supervision of information disclosure and reduce listed costs and inside trading.