A new method using image series of monocular optical imaging system on motion platform for spacecraft orbit determination is developed in the absence of position or velocity information of target spacecraft. Through analysis of characteristics about the imaging system and space relation of the imaging system and the spacecraft, the concept on the real average angular velocity and the apparent average angular velocity is presented to design an equation in order to estimate slope distance of the imaging system according to longitude and latitude data derived from image series and to calculate spacecraft initial state parameters. This method offers an approach for orbit determination with series image from the monocular optical imaging system by coping with the problem to calculate the longitude and latitude according to image series and then to estimate the slope distance. Finally a simulation instance of a GEO satellite is adopted to validate this method.