Fly ash collected after burning coal can replace part of cement and improve the performance of concrete. In this paper, the effect of adding biomass ash to fly ash on the mechanical properties of concrete was studied. The difference of mechanical properties of the concrete made of straw-burning ash mixed with fly ash, wood-burning ash mixed with fly ash and wood-burning ash only partially replacing cement was studied. Results show that using biomass ash to replace 25 wt% cement, the compressive strength (from 1 day to 56 days) and flexural strength (from 56 days to curing) of the concrete made of straw-burning ash-doped fly ash and wood-burning ash-doped fly ash had similar mechanical properties to that of the concrete made with fly ash alone in the blank control group. This provides a reasonable method for the efficient utilization of biomass and a theoretical support for the use of unconventional raw materials in the preparation of concrete.