The structural evolution of lead-free piezoelectric bismuth sodium titanate (BNT) coatings with excess Bi derived from thermal spray process was investigated with transmission electron microscopy (TEM). Bi-rich composition was identified as the nucleation agent of the BNT perovskite phase, and fine-grained microstructure was obtained with more excess Bi. The Bi-rich composition of the perovskite phase crystallized from melt was BixNayTiO3 (0.5 <= X <= 0.55, 0.46 <= y <= 0.5). The crystallization of the Bi-rich BNT perovskite phase first from liquid precursor phase would result in continuous depletion of Bi composition in the residual amorphous phase, and thus Ti-rich amorphous phase in the as-deposited coating and sodium titanate secondary phase in the heat-treated coating formed in the composition without enough access Bi. The results and analyses suggest only appropriate compensation with adequate amount of excess Bi can realize single perovskite phase in thermal sprayed BNT-based coatings and hence the superior piezoelectric performance property.