In this paper, the physical layer network coding is applied into wireless sensor network for secret data transmission. The source node will send the gathered data to the sink node with help of multiple relay nodes. By applying the physical layer network coding, the received signal at the relay nodes is guaranteed to be a summed signal which cannot be separated. Thus, the attack from untrusted relays as well as external eavesdroppers can be prevented. Two types of coding algorithm has been discussed, one for BPSK coding and another for nested lattice coding. Analysis is also conduct for the proposed protocol. In the view of transmission, the proposed protocol can achieve the same time slots cost as the non-security protocol. In the view of security, the proposed protocol can successfully against the attacks identical with cryptography approach, however less hardware and computational complexity will be consumed for the proposed protocol.