Combining the development and utilization of bioenergy with carbon capture, utilization and storage (BECCUS) is one of the important methods to reduce CO2 emissions in the energy field as it can achieve the negative carbon emissions. Biomass ash (BA) generated from the direct combustion of biomass, can be used to absorb and sequestrate CO2 permanently. However, the issue adopting biomass ash to achieve the negative carbon emissions should be investigated carefully. CO2 mineralization performance of biomass ash from atmospheric CO2 and CO2-rich gas streams with a moderate (101.3kPa) and high CO2 partial pressure (300~1400kPa) was experimented in terms of CO2 sequestration capacity. Moreover, negative carbon emissions of these three mineralization pathways were evaluated as well. Results showed that among all the three pathways, the lowest CO2 sequestration capacity with 60.66g/kg after 40 days was acquired when CO2 came from atmosphere. Comparatively, when the initial CO2 partial pressure was elevated to about 101.3kPa (i.e., the moderate CO2 partial pressure case), the maximum CO2 sequestration capacity of 121.68g/kg can be achieved. When CO2 partial pressure was increased to about 1400kPa (i.e., the high CO2 partial pressure case), a CO2 sequestration capacity of 216.85g/kg was obtained. The actual negative carbon emissions of three mineralization pathways of biomass ash were assessed by comparing CO2 emissions reduction ascribed to CO2 sequestration of biomass ash and CO2 emissions related to energy consumption in the mineralization process and biomass ash transportation. When the transportation distance of biomass ash was less than 207km, adopting this mineralization pathway in which CO2 came from the CO2-rich gas streams with a moderate CO2 partial pressure (101.3kPa) might be reasonable for achieving a highest negative carbon emission. When the transportation distance was above 207km, the pathway in which CO2 came from the gases with a high CO2 partial pressure should be sensible.