A method of evaluating and diagnosing performance of an operating wireless sensor network without disturbing or burdening the network is disclosed. The operating wireless sensor network includes a plurality of operational nodes. A system, which comprises a plurality of detecting nodes and a performance evaluation and diagnosis platform, is provided in order to implement the present method. After time synchronization, the detecting node is connected with an operational node. After the detecting node estimates MAC or network layer address of its corresponding operational node, it will capture any transmission of or around the operational node, and upload captured packets to the evaluation and diagnosis platform. The evaluation and diagnosis platform produce a report by analyzing the acquired information from all detecting nodes.