Ross pair and filters stack spectrometers are commonly used to detect hard X-ray spectra. The results of filters stack spectrometer are highly sensitive to the profile of the pre-estimated spectrum, while Ross pair is limited to discrete spectrum. Here we provide a Ross pair-filters stack mixed spectrometer, which combines the advantages of traditional filter stack spectrometers and Ross pairs. Each layer of the filter in the traditional filters stack spectrometer has been replaced with a Ross filter pair. Thus, the discrete spectrum given by Ross pair can be used as the pre-estimated spectrum for the filters stack to solve the entire X-ray spectrum. Numerical and physical experiments using X-ray tube confirm that the present mixed spectrometer can provide more accurate spectral structures compared to traditional filter stack spectrometers. The compact and lightweight design make it widely applicable in hard X-ray spectral measurements.