A harmonic blazed grating was proposed.It can realize multi-wavelength or broadband slanted-beam coupling with high efficiency.Theoretical analysis shows that the number of working wavelength will increase with the increment of the harmonic number of the harmonic blazed grating.As a result,multi-wavelength beam coupling with high efficiency can be realized.If the harmonic number is large enough,broadband beam coupling with high efficiency can be realized.Multi-wavelength coupler and broadband coupler are designed through harmonic blazed gratings,respectively.The theoretical diffraction efficiency is 100% for multi-wavelength coupler and greater than 80% for broadband coupler.