The U-value is a very important parameter for evaluating the energy efficiency when refurbishing the existing buildings.Traditional in-situ test methods to determine the U-value usually require a very long time to filter weather fluctuations and other boundary condition influences.In this paper,the possibility of a new method to reduce the time necessitated for measuring the accurate U-value of a wall is tested.The proposed method recommends measuring the temperatures and heat flux on both sides of the wall and thereby utilising the average values of the internal and external heat flux to calculate the U-value.Under the idealised sinusoidal internal and external air temperature boundary conditions,four walls with different U-values were simulated according to the admittance procedure(AP).Results show that the proposed method could improve the maximum error level for most of the walls in consideration.It was not sensitive to the measurement start time and it was more stable even in less controlled boundary conditions involving large inner temperature variations or out of phase temperature waves.Besides,the error of the average heat flux method(within 10％)could be estimated earlier than that of traditional method.