Since the element’s own characteristic X-rays with low atomic number and the characteristic X-rays between different elements interfere with each other, the measured spectra will be seriously overlapped due to the limitation of the energy resolution of the instrument. In this paper, chromatographic resolution Rs is used to calculate the separation degree of spectral peaks. Taking the overlapping peaks with Rs below 0.5 as the research object, a new method of decomposing low-resolution overlapping peak by using a peak sharpening method combined with the double-tree complex wavelet transform method is proposed, which is verified by decomposing the simulated X-ray fluorescence spectra and the measured X-ray fluorescence spectra. First, based on the principle introduction of the peak sharpening method and the double-tree complex wavelet transform to decompose overlapping peak in detail, the simulation results showed that when Rs=0.38, both methods can not decompose the overlapping peaks with low-resolution separately. However, the spectrum processed by the peak sharpening method not only retains the peaks position characteristics of the original spectrum, but also has the phenomenon that the resolution becomes larger. Therefore, it can realize the initial sharpening of the low-resolution overlapping peak by adjusting the weight of the peak sharpening method, then, using the double-tree complex wavelet transform is performed on the sharpened spectrum. The results showed that the simulated overlapping peak is decomposed. It is proved that the new method is superior to the decomposition of low-resolution overlapping peak. Wherein, the decomposing level of the double-tree complex wavelet is set to 2~6, the first level selects the near_sym_b filter, the higher level selects the qshift_d filter, and when the detail coefficient magnification is set to 1~10, the decomposing results of the overlapping peak is more accurate. Second, the overlapping spectrum of the Kα energy peak and the Kβ energy peak of K (Rs=0.44) and the overlapping spectrum of the Kβ energy peak of Fe and the Kα energy peak of Co (Rs=0.34) are simulated. The new method is used to decompose the spectra, and the two overlapping spectra are decomposed. The relative error of peak position and peak area of the decomposed spectra is within 1% and 6% respectively, which verified the feasibility of the new method to decompose the low resolution overlapping peaks in the spectrum. Finally, the actual measurement Ca X-ray fluorescence spectrum is decomposed by a new method, and the errors of the peak position are 0.8% and 0.7% respectively. The results showed that the peak sharpening method combined with the double-tree complex wavelet transform can effectively decompose the low-resolution overlapping peaks, and it has practicality in solving the problem of severe overlapping of X-ray fluorescence spectra.