A method to accurately locate projected center point from single circle image is proposed based on crossratio invariance principle and geometric constraint conditions in projective transformation. Take arbitrary circle secants, the relationship between the secant midpoint and the point at infinity is clear according to the harmonic conjugates and cross-ratio invariance. The equations which contain parameters of secant midpoints are established for solving secant midpoints based on the geometric constraints. Then the position of projected circular center is calculated. Compared with taking the center of projected ellipse as the center point directly, the proposed method does not have projection error. Simulation experiment results show that the accuracy and stability of the method is superior to the method of extracting ellipse′s center. The results of actual experiment show that the circular center positions are consistent with the positions extracted from the relationship among multiple circles, and the maximum position error does not exceed 0.8 pixel. The proposed method can locate the center of a single projected circle independently, which is suitable for wider applications.