To increase the efficiency of eavesdropping detection in the “Ping-pong” protocol, an improved secure detection strategy based on W states in “Ping-pong” protocol is presented. TheWstate, the decoy particles, is used to detect eavesdroppers. In the experiment, the method of the entropy theory is introduced, and three detection strategies are compared quantitatively by using the constraint between the information which eavesdropper can obtain and the interference introduced. If the eavesdropper intends to get full information, the detection rate of the original “Ping-pong” protocol is 50%; the second protocol is also 50%; and the presented protocol 58%. The experimental result shows that the efficiency of eavesdropping detection in the presented protocol is higher than the other two, so the detection strategy in the protocol can ensure the “Ping-pong” protocol more secure.