In order to improve the spot position detection performance of four-quadrant detector (QD), the main factors affecting QD position detection accuracy in the Gaussian spot model are studied. The basic principle of QD position detection is analyzed. Then on the basis of error theory, the mathematical model of the relationship between position detection accuracy and spot radius, centroid position, signal to noise ratio (SNR) is obtained when a laser spot of Gaussian energy profile illuminates QD. The validity of mathematical model is verified by numerical simulations and experimental analysis. The trends and degree of the factors impact on the position detection accuracy are further discussed. The results show that adoption of smaller spot radius, closer to the center of photosensitive area, and higher SNR, can effectively improve the accuracy of spot detection when the detection range of QD system is fixed. When system′s SNR is 57.48 dB and spot radius is 0.6 mm, the center position detection accuracy of QD can be up to 0.514 μm.