Environmentally friendly antiferroelectric NaNbO₃ (NN) materials exhibit promising potential in energy storage and electro-strain applications. At room temperature, NN is an antiferroelectric P phase (Space group Pbma) that coexists with a metastable ferroelectric Q phase (Space group P2₁ma), so the electric field-induced phase transition is irreversible. To stabilize the intrinsic antiferroelectric properties of NNs, phase structure regulation has emerged as a critical research focus. We chose the variable-valence elements Sn and Ce for doping in NN. Through atmospheric sintering, the valence states of the doped ions were altered, resulting in changes in their corresponding substitution positions. This confirmed that the doped ions could be successfully incorporated into the lattice as designed. Importantly, the x = 0.04 ceramic exhibited a reversible phase transition between the AFE and FE states, resulting in a standard double hysteresis loop at room temperature and a large electrostrain of 0.38%. These findings demonstrate that valence state-controlled co-doping effectively optimizes the antiferroelectric phase stability and functional performance of NN-based materials.