Instability is a notable feature of wire-array Z-Pinch. The magneto-Rayleigh-Taylor instability is the most dangerous instability in destroying the symmetry of the pinch. The stage of electrically exploding wires has critically impact on the stability, quality of imploding and X-ray yield of wire-array Z-Pinch. The electrothermal instability couples to the subsequently magneto-Rayleigh-Taylor instability and severely restricts the performance of wire-array load. The experiments characterizing the stratified and filamentary structures formed in the dense core of nanosecond electrically explosion of aluminum wires to understand the evolution mode for electrothermal instability are reported. The occurrence of different modes of electrothermal instability is discussed based on experimental measurements. In order to predict the physical scenario of electrothermal instability, a computational model within the framework of resistive magnetohydrodynamic regime with two-temperature approximation is constructed. The computational model embeds a wide range equation of state and transport coefficient to describe the phase transition of metallic load. Numerical investigation on the evolution of stratification instability seeded by resistive inclusions in electrically exploding aluminum wires is carried out. The resistive inclusions at the submicrometer scale create hot spots with enhanced Joule heating during the first phase of electrical explosion. A numerical shadowgram is reconstructed using a flow visualization technique. The matching of the numerical shadowgram and experimental shadowgram indicates that the resistive inclusions characterized by increased resistivity comprise an important seed in stratification instability. This study helps in understanding the seeding mechanism of electrothermal instability in pulsed-power-driven plasma systems.