Abstract: Group mobility is the typical mobile mode in tactical Ad hoc networks. The characters of groups confine the shaping of zones for Zone Routing Protocol (ZRP) and affect the routing performance greatly. The introduction of location information can improve these. Position Based Modified ZRP (PBMZRP) effectively triggers the neighbor nodes update process of IntrAzone Routing Protocol (IARP) in virtue of node positions, accordingly the broadcast overhead has been decreased much. While, the network diameter restricts the length of routing enquiries during IntErzone Routing Protocol (IERP). Simulation results show that under the circumstance of group mobility, PBMZRP has better performances in the case of delay, throughput, etc.