Accurate estimation of moving target's postion is a very important research area of optical measurement since it has to be performed in many applications. Under the condition that there are no range information of target and known points on the target, such an assumption is made that the target obeys a movement rule is made which adds extra information for target positioning. For moving target positioning under the condition of monocular camera, a new method, collinear equation method, is proposed. The correctness and feasibility of the method are proven by simulation data.