Currently, a cloud database is employed to serve on-line query-intensive applications. It inevitably happens that some cloud data nodes storing hot records are facing high frequent query requests while others are rarely visited or even idle. Therefore, how data are dynamically allocated and migrated at runtime has significant impact on query load distribution and system performance. Existing system adopt centralized approaches, and they face two main challenges: (1) Query load on individual node cannot be always balancing even if the data are fairly distributed; (2) For each node, the dynamic changes of configuration resources cannot be captured during the runtime. To this end, this paper presents an environment-aware market strategy based system, named e-MARS, for reasonable data migration to achieve query load balance in cloud database. In e-MARS, cloud database is modeled as a cloudDB market, while data nodes are regarded as intelligent traders and the query load as commodity. Each trader is aware of its local environmental re-sources, such as computing capacity, disk volume, based on which the trader itself decides how to trade the query load and migrates the corresponding data. In this way the cloudDB market will achieve equilibrium. Experiments are conducted on the real communication data, and e-MARS significantly enhances the efficiency. Compared with HBase Balancer, more than 65% improvement is achieved in terms of query response time.