In order to study the effects of different mass dosage of triethanolamine (TEA) as grinding aid on the particle properties of bagasse ash, the particle properties of bagasse ash were characterized by sieve residue test, BET, particle size distribution test and particle shape test, the effects of bagasse ash particle properties on the strength and chloride resistance of bagasse ash mortar were investigated. The results show that TEA optimizes the particle size distribution of bagasse ash, and the proportion of particles smaller than 32 μm increases by 8.2 percentage point, the specific surface area increases to 5.503 5 m2/g, and the particle shape tends to be spherical under the optimal addition of 0.08% (mass fraction).Meanwhile, the strength and chloride resistance of bagasse ash mortar show a pattern of increase first and then decrease with the increase of TEA content; the compressive strength of bagasse ash mortar increases by 19.88% and the chloride ion diffusion coefficient drops by 79.63% compared with normal concrete when TEA dosage is optimally at 0.08%. The mechanism of the influence of bagasse ash particle properties on the performance of bagasse ash mortar is revealed by X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). Results show that the pozzolanic activity of bagasse ash optimized by TEA is enhanced, and more hydration products are generated in the bagasse ash mortar matrix to improve the compactness. The optimized bagasse ash particles give full play to the filling effect, reduce the void ratio of bagasse ash mortar, and improve the the mortar strength and resistance to chloride salt erosion.