Advances in technology have promoted offshore wind energy being one of the most promising renewable energy sources. Offshore wind farms are usually positioned in an opened space far away from the seashore where the wind is strong enough to generate electricity effectively and reliably. However, due to location characteristic hard–to–reach, the operation and maintenance cost of the offshore wind farms are high and the economic evaluation is uncertain. A huge number of researches about offshore wind energy have emerged recently in response to these issues. However, the researches considering the effects of various influential parameters to access the reliability of offshore wind turbine remain small and still limited, especially the parameters related to the dynamic weather conditions such as real-time utilization under typhoon and flood impacts. This paper proposes an approach to analyze the life–cycle–cost of the offshore wind turbines under maintenance scenarios and environmental influences, with the support of probabilities distribution method. The electricity generated by the offshore wind turbine is calculated based on the real weather conditions collected in a variety of locations throughout Taiwan such that the proposed life–cycle–cost model is more reliable and accurate than the conventional approaches. The results show that Typhoon and Maintenance cost occur 4.2% and 19.6% respectively. Moreover, offshore wind energy is an excellent environmental solution with high economic benefit on sites where the wind resource is abundant.