In this paper we have conducted a comprehensive measurement and analysis on the Dream market, an anonymous online market that uses cryptocurrency as transaction currency. We first collect data between October 30th 2018 and March 1st 2019. Then we use decision tree-based approach to classify goods. Following we analyze the category of goods sold in the market, the shipping place of vendors. By analyzing more than 1,970,303 items, we find the goods sold in Dream Market are mainly drugs and digital goods. We estimate the total sales of all vendors, and find that an average monthly income is $14 million during the measurement period, which means that the market commission income is more than $560,000 per month. Based on these data, we use transaction cost theory to analyze the transaction attributes of illegal transactions, which shows that anonymous online market can reduce transaction cost of illegal transactions. We finally discuss the results analyzed and the intervention policy, as well as recent DDoS attacks and future trends of illegal transactions in anonymous online market.