In wireless sensor networks, the adversary can easily control the compromised nodes to inject false data reports. En-route filtering is an effective mechanism to resist such attacks, where the forwarding nodes of the reports can identify and drop the false reports. However, the existing en-route filtering strategies are vulnerable to report disruption attacks and selective forwarding attacks, and the probabilities and efficiencies of en-route filtering false reports are low. To address these problems, a precheck mechanism performed by the CoS (Center-of-Stimulus) node is presented to resist report disruption attacks, a report forwarding strategy with balancing the residual energy of the nodes is designed to resist selective forwarding attacks, and an en-route message authentication scheme (EMAS) based on monitoring and reporting mechanism is proposed to resist false data injection attacks. The theoretical analysis and simulation results show that in most cases, EMAS provides a higher security level and higher en-route filtering probability and efficiency and is very efficient in energy saving.