Abstract: A novel method for modifying a turbofan aeroengine into a land-base turboshaft engine was proposed by late Prof.C.H.Wu.In this case,the exhaust of hot core flow is used to recuperate the bypass flow,therefore,it is not necessary to redesign the low pressure compressor (fan) and the low pressure turbine.A comprehensive thermodynamic analysis is given to study the applicable range and results of this proposal.It is found that such modification is suitable for the turbofan engines with bypass ratio approximately equal to 1.The optimum total pressure ratio for efficiency is rather low and approximate to the optimum pressure ratio of pure gas turbine for specific output.The obtainable system efficiency and power can be higher than the conventional modification method (cutting the top of fan blade) for about 10% relatively.