The constraints induced by prohibited zones (PZs) were traditionally formulated as multiple disjoint regions. It was difficult to solve the optimal power flow (OPF) problems subject to the disjoint constraints. This paper proposes a new formulation for the OPF problem with PZs. The proposed formulation significantly expedites the algorithm implementation. The effectiveness of the new approach is verified by different methods including traditional optimization methods, PSO and particle swarm optimization with adaptive parameter control which is conducted on the IEEE 30-bus test system.