Military Heterogeneous Wireless Sensor Network (MHTWSN) is an emerging technology. Due to its extending services, MHTWSN is becoming a widely preferable network for border area monitoring and enemy object tracking in sensitive, unmanned areas. However, security is one of the key challenging issue in MHTWSN. Many routing protocols like AODV, AOMDV, I2MR, and IMCC have proposed for efficient routing establishment and data delivery, but these routing protocols results the poor performance when the network is under any security attack. So we have proposed a new secure multipath routing protocol (NSRP) for military heterogeneous wireless sensor network (MHTWSN) for secure data transmission. NSRP uses elliptic curve cryptography (ECC) to discover trusted neighbor nodes and establish the secure multiple routes for reliable data delivery in MHTWSN. Our protocol has an efficient key management mechanism which provides better security and improves the network performance. NSRP has achieved low communication overhead, memory requirement and energy consumption as compared with existing key management schemes.