The dim photoelectrical target in space has the weak signal energy. If the target motion parameters and brightness information were lack in the low Signal to Noise Ratio (SNR) conditions, it would be difficult to achieve the detection and tracking of dim target. Due to the character of particle filter in the signal processing, its application in the dim target tracking was researched. First, the basic theory of particle filter in the application of the tracking was analyzed. For the tracking of target with unknown luminance, a method for constructing the objective function via point spread function was presented, and the weight of the particles could be updated. Then, by using the circular orbit as the circulating model of target, the speed range of the space target on the sensor was estimated, thus optimizing the initial conditions for the particles. Finally, a simulation experiment for tracking the dim target was made to testify the effect of this method on decreasing the number of particle.