Abstract: ‍ ‍In order to solve the problem that the existing radar equation is not consistent with the reality in evaluating the maximum detection range of sea-to-sea radar， a method is proposed to modify the equation based on the general equation and the measured data. The limitation of the application of the general radar equation is analyzed， and the general equation is simplified to signal-to-clutter ratio equation according to the influence of sea clutter on target detection. The equation of signal-to-clutter ratio is modified by using the experimental data of X-band sea detection radar， which overcomes the deficiency of the equation in practical application and satisfies the calculation of the maximum detection range of the target by this type of radar. The results show that the results calculated by the modified equation are basically the same as those shown by radar.