To improve the accuracy of the static contact angle measurement in the silicone rubber aging experiments, a high accurate contact angle algorithm in combination with the circle fitting algorithm and ellipse fitting algorithm is proposed. The influence of the water drop volume and noise on the calculation accuracies of the two algorithms are analyzed. The results reveal that the circle fitting algorithm is more suitable for the images with small water drop volume and contact angle. However, the ellipse fitting algorithm is more suitable for the images with relatively large water drop volume and contact angle. The critical water drop volumes of the two algorithms in different hydrophobicities are obtained by the calculation of contact angle by the two algorithms. And it is used to select which algorithm to calculate contact angles in the proposed algorithm. The tangent line method, θ/2 method, circle fitting algorithm, ellipse fitting algorithm, and proposed algorithm are implemented. The numerically generated water drop profiles and real water drop images of aged silicone rubber are used to validate the new algorithm. The results indicate that the proposed algorithm is more accurate than the other algorithms in different water drop volumes, contact angles, and noise levels.