In inter-satellite laser communication, four-quadrant detector is often used in precise tracking unit for spot location. The positioning error directly affects the angular measurement accuracy of fine tracking unit. In order to achieve the tracking precision of micro-radian magnitude, this paper studies various noise factors that affect the positioning accuracy of the detector, simplifying the analysis according to the practice of inter-satellite laser communication, and putting forward the specific calculation method of positioning error. Finally, we evaluate the influence degree of each factor through a specific example. The results show that the signal-to-noise ratio of the received signal increases with the increasing of emitting power in a certain range with reduced positioning error. However, positioning error does not decrease linearly with the increase of transmitting power. When the transmitting power increases to a certain extent, the reduction of tracking error is limited. At this time, it will be very expensive to improve the tracking precision simply by increasing the transmitting power.