Abstract: In order to realize the transformation of naval gun from task to capability in anti-sea combat, the framework model of capability requirement was established. The paper analyzed the mapping relationship between sea combat task and combat capability based on the naval gun combat process. According to the mapping relationship, the mathematical models of the detection probability, maximum detection distance, reaction time and single-shot probability were established. The simulation experiment analyzed the capability requirements of the new naval gun at different firing distances with the fire control system accuracy when shooting at 20 km as the standard under the variable initial velocity of new naval gun, and analyzed the change trend of the capability index at different initial speeds. The result shows the higher precision of fire control system, the greater single-shot probability. For targets within sight distance, the higher the initial velocity, the better the single-shot probability. But the advantage of initial velocity is not obvious for long distance targets. The method has important theoretical and practical significance for scientific development of naval gun weapon equipment.