High-performance solid electrolytes are critical for realizing all-solid-state batteries with enhanced safety and cycling efficiency. However, currently available candidates (sulfides and the NASICON-type ceramics) still suffer from drawbacks such as inflammability, high-cost and unfavorable machinability. Here we present the structural manipulation approaches to improve the sodium ionic conductivity in a series of affordable Na-rich antiperovskites. Experimentally, the whole solid solutions of Na3OX (X = Cl, Br, I) are synthesized via a facile and timesaving route from the cheapest raw materials (Na, NaOH and NaX). The materials are nonflammable, suitable for thermoplastic processing due to low melting temperatures (<300 degrees C) without decomposing. Notably, owing to the flexibility of perovskite-type structure, it's feasible to control the local structure features by means of size-mismatch substitution and unequivalent-doping for a favorable sodium ionic diffusion pathway. Enhancement of sodium ionic conductivity by 2 magnitudes is demonstrated by these chemical tuning methods. The optimized sodium ionic conductivity in Na2.9Sr0.05OBr0.6I0.4 bulk samples reaches 1.9 x 10(-3) S/cm at 200 degrees C and even higher at elevated temperature. We believe further chemical tuning efforts on Na-rich antiperovskites will promote their performance greatly for practical all-solid state battery applications. (C) 2015 Elsevier B.V. All rights reserved.