ns2-Metal halide perovskites have attracted wide attention due to their fascinating photophysical properties. However, achieving high photoluminescence (PL) properties is still an enormous challenge, and the relationship between the lattice environment and ns2-electron expression is still elusive. Herein, an organic-inorganic Bi3+-based halide (C5H14N2)2BiCl6·Cl·2H2O (C5H14N22+ = doubly protonated 1-methylpiperazine) with a six-coordinated structure has been successfully prepared, which, however, exhibits inferior PL properties due to the chemically inert expression of Bi3+-6s2 lone-pair electrons. After reasonably embedding Sb3+ with 5s2 electrons into the lattice of (C5H14N2)2BiCl6·Cl·2H2O, the host lattice environment induces the Sb-Cl moiety to change from the original five-coordinated to six-coordinated structure, thereby resulting in a broad-band yellow emission with a PL efficiency up to 50.75%. By utilizing the host lattice of (C5H14N2)2BiCl6·Cl·2H2O, the expression of Sb3+-5s2 lone-pair electrons is improved and thus promotes the radiative recombination from the Sb3+-3P1 state, resulting in the enhanced PL efficiency. This work will provide an in-depth insight into the effect of the local structure on the expression of Sb3+-5s2 lone-pair electrons.