TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The polyol benzoate is phenylformic acid diethylene glycol ester and/or phenylformic acid dipropylene ester. The dialkyl benzenecarboxylate is di-iso-octylphthalate, terephthalic acid diamyl ester and/or isophthalic acid dicaproic acid ester. The alkyl polyprotic acid ester is dioctyl azelate, trioctyl trimellitate, dioctyl sebacate, di-n-octyl adipate and/or dibutyl ester.    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: Before the mixing step, the method comprises vacuum deaerating polyamic acid, pore-forming substances and solvent at 15-40 degrees C for 1-12 hours with vacuum degree of 0.001-0.1 MPa. After forming the mixture, the method comprises coating the mixture to supporting body at 10-40 degrees C and relative humidity of 20-80, and drying to remove solvent. The imidization step is carried out at 70-300 degrees C for 0.5-5 hours, and then at 300-450 degrees C for 0.5-4 hours. The method may utilize a mixture tetracarboxylic acid dianhydride, organic diamine and solvent prepared at 20-70 degrees C for 3-15 hours. Preferred Components: The tetracarboxylic acid dianhydride and the organic diamine are at mole ratio of 0.8-1.2. The porous film comprises tetracarboxylic acid dianhydride and organic diamine, and pore-forming substances at weight ratio of 1:0.01-0.3, and the tetracarboxylic acid dianhydride and organic diamine, and the solvent are at weight ratio of 1:4.5-10. The polyamic acid is poly(itaconic acid monomethylester), poly-biphenyls tetraformamide acid and polybenzophenone tetraformamide acid; the solvent is chosen from one or several of N-2-methylpyrrolidone, N,N-dimethyl acetamide, tetrahydrofuran, N,N-dimethyl formamide, cresol, dimethyl sulfoxide or methanol. Preferred Properties: The polyimide porous film has aperture distribution comprising pore diameter of 70-400 nm (greater than 75%), and pore diameters of less than 70 nm and greater than 400 nm (less than 25%). The polyimide porous film has breathability of 10-200 s/100 cc, and thickness of 8-30 mu m. The polyamic acid has inherent viscosity of 100-200 (preferably 140-190) ml/g,