In　order　to　ensure　wind　turbine　running　safely　and　steadily　in　complicated　environment,　a　probabilistic　model　for　analysis　of　the　failure　of　a　wind-turbine　rotor　blade　in　flap-wise　bending　is　presented.　This　model　capitalizes　on　stress-strength　interference　theory　and　curve,　and　Weibull　model　about　the　wind＇s　distribution　is　considered.　This　model　accounts　for　the　uncertainties　about　the　loads　acting　on　the　wind-turbine　rotor　blade　by　the　unstable　wind　distribution.　A　20-year　design　lifetime　is　assumed.　The　probability　of　fatigue　failure　in　flap-wise　bending　of　the　rotor　blade　is　calculated　by　means　of　a　first-order　reliability　method.　Four　situations　are　calculated　when　turbulence　intensities　are　0.02,　0.1,　0.15,　0.2　and　wind　velocity　is　12　m/s.　Conclusions　can　be　drew　through　comparison:　linearity　of　Gumbel　distribution　is　better　than　one　of　three-parameter　Weibull　distribution　and　Weibull　distribution,　because　the　two　distributions　have　some　tails.　At　last,　Stress-strength　Interference　Theory　model　is　validated　by　600　kW　wind　turbine　blade.　Conclusion　has　shown　that　wind　turbine　rotor　blade　can　meet　the　design　standards.