A new design method with good applicability and easy to implement in technology is presented for broadband metallic diffraction gratings with single blaze surfaces. In consideration of the principles of two types of grating anomalies,Rayleigh type and resonance type,the occurrence conditions of the grating anomalies are discussed. On the basis of electromagnetic theory of gratings,the blaze characters of diffraction efficiency both for TE and TM modes are numerically analyzed,and the relationships among the grating anomalies,the spectrum bands of gratings and the blazed wavelengths is obtained. An idea of designing diffraction gratings is proposed to compensate the Rayleigh anomaly or resonance anomaly with the first blazed wavelength of TM mode. It is pointed out that the compensating effect of the first blazed wavelength of TM mode to Rayleigh anomaly is only the limitation case to the resonance anomaly. The design examples of broadband metallic gratings with different groove densities applied in UV-visible and infrared spectrometers are given.Experiments indicate that the diffraction efficiency of the broadband methallic grating has been over 40% in different spectral bands,which shows that the compensating effect method is better than traditional design methods of broadband metallic gratings,whether in theory design or technology process.