Based on analyses about system effectiveness of the weapon and aiming at application requirements from the weapon type approval tests, a modified ADC(availability-dependability-capability) method was put forward in order to solve the problem that the actual usability of the weapon cannot be presented accurately and entirely by dividing system conditions using the traditional ADC method. Comprehensive modifications were performed, such as putting forward the strategy of adding the medial conditions in the model. As the results showed, functions for integrating the sub-system effectiveness, for describing and computing the conditions, for transfers between conditions, and for capabilities were all improved. A software platform SEEK was developed based on these modifications. System effectiveness evaluation of a main tank was selected as an example for demonstrate feasibility and validity of the method.