The 2-D slit array mask is a new design of Hadamard spectrometer mask. Having discussed the influence of the inconsistency caused by the machining errors in the size and location between the slits in the same column on the wavelength accuracy of the Hadamard spectrometer, the authors bring up with the way to decrease the influence on the wavelength accuracy of the spectrometer caused by the difference in the height and location vertical to the spectrum between the slits in the same column, and then estimate the spectral shift caused by the relative location shift along the spectrum between the slits in the same column. A model for simulation was built, and the measurement errors in the decoded spectrum generated by one column of the slits on the mask were calculated, when there are inconsistency errors in width and location along the spectrum between the slits in another column. Based on the simulation calculation, we can determine the machining precision of the mask. The research will be meaningful to the design of the 2-D slit array mask using MEMS(micro-electro-mechanism system) technique and the revise of the decoded spectrum, which can provide the spectrometer with a reasonable wavelength accuracy.