Abstract: The method of Wavelet Transform Modulus Maximum(WTMM)is used to study the multi-fractal properties of temperature data in Rayleigh-Bénard convection. With wavelet transformation, the coherent structure involving temperature data is extracted. By the definition of a so called non-coherent signal(the original signal minus coherent signal), the influence of coherent structure on the multifractal spectrum D(h)and the relation between large scale motions and small ones are highlighted. It is concluded that the large scale coherent motions do not have almost any influence on D(h)which can only be seen at small scale structures. In this sense, the multifractal spectrum D(h)is invariant.