Herein, the structural, optical, electronic and thermoelectric properties of the NaAs3P5 were investigated by Ab-initio calculations. The electronic results of NaAs3P5 showed that this compound has a metallic characteristic. The optical response of this compound has been studied using optical parameters such as complex dielectric function, refractive index, optical conductivity, electron energy loss, and absorption coefficient. This compound is an n-type material, as determined by thermoelectric experiments because it has a negative Seebeck coefficient when the strain is at 20 %. The highest value of the figure of merit (ZT) is about 0.021. Besides, the obtained value of PF is 7595.5 W−1.K−2.s−1 for 20 % of the strain. As the ZT trend grows, the alloy is being promoted as a potential contender for thermoelectric power production. Applying dilatation strain can improve the mechanical and thermodynamic stability of NaAs3P5 because many solid-state physical characteristics, such as heat capacity, thermal expansion coefficient, and entropy, are related to the Debye temperature.