The invention discloses a heat-shrinkage-resistant lithium ion battery diaphragm and a pore-forming agent composition adopted by the same. The pore-forming agent composition comprises an organic pore-forming agent and an inorganic pore-forming agent, wherein the organic pore-forming agent is high-boiling-point low molecular weight organic matter preferably; the inorganic pore-forming agent is water-soluble inorganic nanoparticles preferably; and the pore-forming agent and the optional additive are jointly added to a film-forming material to form a lithium ion battery diaphragm with three kinds of microporous structures through processing of casting pieces. In addition, the heat-shrinkage-resistant lithium ion battery diaphragm has relatively low closed-hole temperature, high heat shrinkage resistance, high tensile strength, high puncture strength and relatively high diaphragm-rupture temperature, thereby ensuring safety in preparation and usage of the lithium ion battery.