The present invention relates to a multi-energy-spectrum X-ray grating imaging system and an imaging method. The multi-energy-spectrum X-ray grating imaging system comprises a non-coherent X-ray source for emitting X-rays for irradiating an object to be detected, a grating module and an energy spectrum resolution-type X-ray detector, the grating module comprises a first absorption grating and a second absorption grating which are configured parallel to each other and arranged sequentially in the direction of propagation of the X-rays, the energy spectrum resolution-type X-ray detector receives the X-rays passing through the first absorption grating and the second absorption grating, one of the first absorption grating and the second absorption grating performs phase stepping movement in at least one period range, in each phase stepping process, the non-coherent X-ray source emits X-rays for irradiating the object to be detected, the energy spectrum resolution-type X-ray detector receives the X-rays and performs energy spectrum resolution of the X-rays, and by one-time phase stepping process and data acquisition, and light intensity of the X-ray of each energy segment of each pixel point on the energy spectrum resolution-type X-ray detector is represented as a light intensity curve.