The spatial light modulation process makes direct effort on imaging data fidelity of the spatial coding compressive spectral imaging. To expand existing coding patterns for spatial light modulation in compressive spectral imaging and reveal its relation it and the imaging data fidelity, the research on coding modulation effect in compressive spectral imaging is carried out. Based on the physical model of imaging system, present binaryzation coding amplitude modulation method is extended, the research on non-binaryzation continuous amplitude modulation is adopted and the phase modulation method is also verified. The root-mean-square error of the full-spectrum images is worked out so that the correlation between modulation coding pattern and the imaging data fidelity is quantitatively revealed. The simulation scenery of certain spatial and spectral features is constructed so that the imaging simulating experiment is carried out. The imaging results under six kinds of spatial coding modulation conditions are compared. The employing feasibility of non-binaryzation amplitude coding modulation is verified and the ralidity of data fidelity improved by the spatial light phase modulation is testified.