Navigation of a group of autonomous agents that are required to maintain a formation is a challenging task which has not been studied much especially in 3-D terrains. This paper presents a novel approach to collision free path finding of multiple agents preserving a predefined formation in 3-D terrains. The proposed method could be used in many areas like navigation of semi-automated forces (SAF) at unit level in military simulations and non-player characters (NPC) in computer games. The proposed path finding algorithm first computes an optimal path from an initial point to a target point after analyzing the 3-D terrain data from which it constructs a weighted graph. Then, it employs a real-time path finding algorithm specifically designed to realize the navigation of the group from one waypoint to the successive one on the optimal path generated at the previous stage, preserving the formation and avoiding collision. Software was developed to test the methods discussed here.