Abstract: The turbo-shaft engine with free turbine can't guarantee similar rule perfectly.For the purpose of engine parameter correction,the traditional resemble correction formula with too much tolerance was discussed.And,a more scientific method called equivalent conversion of turbo-shaft engine parameters correction based on simulation was brought forward.Finally,an example was presented.The results show that,this new method can be used to reduce the tolerance of the performance parameter correction,laying a foundation for formulating the turbo-shaft engine test performance modification standard and acceptation specification.