The present invention relates to a thermoelastic polyolefin-based elastomer sheet composition for water based coating treatment, which comprises a partially crosslinked thermoelastic polyolefin-based elastomer resin, a non-crosslinked thermoelastic polyolefin-based elastomer resin, a polypropylene resin, an ethylene octene rubber resin, a linear low density polyethylene resin, polyethylene master batch containing a lubricant, and an inorganic filler, the composition being useful for vehicular inner parts (e.g., crash pad) due to its superior elongation, heat resistance, humidity resistance and molding property.