Due to the sensitivity of traditional Monte Carlo simulation (MCS) in tackling with rare event, this paper presents a new Monte Carlo simulation approach based on cross-entropy (CE) method to evaluate the generating system adequacy. The basic idea is to use a new importance sampling density function, whose parameters are obtained from an optimization process that minimizes the computational effort of MCS approach. The IEEE Reliability Test System is used to test the proposed methodology, and also various modifications of this system are created to fully verify the ability of the proposed approach against the traditional MCS. The comparison demonstrates that the proposed CE-based MCS method improves the calculation speed greatly while ensuring the evaluation accuracy.