The force distribution coefficient is introduced according to the principle of the stiffness distribution; a method of calculating the horizontal stiffness coefficient of the ring support system is developed, and its analytical solutions are derived; furthermore, the revised analytical solutions are given. The procedure is employed to calculate the horizontal stiffness coefficient of the ring support system of an extra deep foundation pit with ring support. The influence of different closed ring beams and transmitting beams on the horizontal stiffness is also analyzed. The calculated results by proposed procedure are compared with those by three-dimensional finite element method. The results show that the error with the two methods is small, and the horizontal stiffness of the ring support system is mainly determined by the closed beam of the force bar, and is trivially affected by the force beam of the transmitting beam. According to the proposed analytical formula, the result is accurate and simple, which can provide the basis for determining the design values of the horizontal stiffness coefficient of the foundation ring support system.