In order to improve the strength and volume stability of plastering mortar, the effects of cement content and ash-slag ratio (mass ratio of CFB fly ash to CFB slag) on 2 h consistency loss rate, compressive strength and volume stability of CFB fly ash and CFB slag plastering mortar were studied. The micro morphology, element distribution and phase composition of mortar were characterized by scanning electron microscope, X-ray energy spectrometer and X-ray diffractometer. The results show that when the cement content is 5%, 8% and 12% (mass fraction), the strength grade of CFB fly ash and CFB slag plastering mortar reaches M10, M15 and M20, respectively. When the content of cementitious material is constant, the 2 h consistency loss rate of mortar decreases with the increase of cement content. And when the content of cement is constant, the 2 h consistency loss rate of mortar increases and the expansion effect decreases with the increase of ash-slag ratio. Expansive ettringite generated in the CFB fly ash and slag plastering mortar fills the pores between the particles effectively, so as to improve the strength and volume stability of mortar.