In this study, the combustion behavior, synergistic effect and ash characteristics during the co-combustion of bituminous coal and wheat straw were fully analyzed by thermogravimetric analyzer, ash melting point analyzer, X-ray diffraction and scanning electron microscope. Thermogravimetry analysis showed that wheat straw was easier to be ignited, showing higher devolatilization activity and lower thermopositive temperature. Co-combustion displayed volatiles and char combustion stage and showed lower combustion rate compared to mono-combustion. For the wheat straw blending ratio≤50%, significant positive synergistic effect was observed during the volatiles combustion stage while negative synergistic effect was found during the char combustion stage. With wheat straw blending, the co-combustion ash fusion temperature first increased and then decreased. The mineral components of co-combustion ash gradually changed from high ash melting point compounds to complex calcium silicate hydrate. The morphology of co-combustion ash turned from hard flake structure to loose porous structure, showing partial melting in the biomass derived pores. Small addition of wheat straw during co-combustion would be beneficial to enhance the ash fusion temperature and optimize combustion performance.