In this paper we study quantitatively the effects of atmospheric turbulence on the measurement sensitivity of a quadrant detecting array, along with the measurement variance induced by atmospheric turbulence. Our results show that the stronger the turbulence strength, the lower the measurement sensitivity, and the larger the measurement variance. This agrees with the experimental phenomena we have observed up to now. In addition, the measurement sensitivity in the X direction could be affected by the deviation of light spots in the Y direction due to the existence of gaps between the quadrant elements. Such effects still exist for the measurement variance even when there are no gaps at all. This effect is analyzed quantitatively.