Query is the main workload of a database system， and its efficiency determines the performance of the database system. There are multiple execution plans for a query， and the existing query optimizers can only statically select a better execution plan for a query according to the configuration parameters of the database system. There are complex and variable resource contentions between concurrent queries， and such contentions are difficult to be reflected accurately through configuration parameters； besides， the efficiency of the same execution plan is not consistent in different scenarios. The selection of the execution plans for concurrent queries needs to consider the influence between queries — query interaction. Based on the above， a metric for measuring the influence of query interaction on the query under concurrent query called QIs （Query Interactions） was proposed. For the selection of query execution plan under concurrent query， a method called TRating （Time Rating） was proposed to dynamically select the execution plan for the query. In the method， the influence of query interaction on the queries executed with different plans in the query combination was measured， and the plan with small influence of query interaction was selected as the better execution plan for the query. Experimental results show that TRating can select a better execution plan for the query with an accuracy of 61%， which is 25% higher than that of the query optimizer； and the accuracy of the proposed method is as high as 69% when selecting suboptimal execution plan for the query.