This paper explores the possibility of using fine iron tailings sand (FIOTS) instead of silica sand (SS) to prepare high-strength alkali-activated mortar (HAAM). Fly ash and slag were used as precursors of alkali-activated materials, the effects of FIOTS/SS mass ratio and curing conditions on the basic mechanical properties of fly ash-slag based HAAM were investigated using MTS universal testing machine, and X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy spectrometry (EDS) were used to reveal the relationship between microscopic phase composition, morphological characteristics and chemical composition of alkali-activated products and macroscopic mechanical properties. The test results show that the compressive strength and splitting strength of HAAM gradually decrease with the increase of FIOTS/SS mass ratio. The highest mechanical properties of HAAM under indoor curing are followed by those under standard curing and under water curing, while the reduction of mechanical properties of the specimens under water curing is more significant with the increase of FIOTS substitution rate. The reduction of mechanical properties of HAAM is mainly due to the inhibition of the alkali-excited reaction process by Fe element in FIOTS, and the formation of mineral phases which are not beneficial to the mechanical properties.