Abstract: Micro-distance spectra splitting is a key technology for compact dual-band imaging system in infrared field. Utilizing the Fresnel diffraction theory and angular spectrum theory, the diffractive properties of dual-wavelength and wide angle light passing through stepped phase grating in fractional Talbot distance were theoretically investigated. A typical scheme of imaging structure based on dual-array detection pixels was set up, where two light beams with different wavelength incident after passing through the stepped phase grating. The numerical simulation shows the splitting results of incident 4 m and 4.5 m wavelength light with-30 to 30 angle, including the distribution of luminous intensity, energy and signal-to-noise ratio on dual-array detection pixels. Our results are beneficial not only for designing the compact dual-band optical imaging structure, but also for building up precision spectral separating component.