The invention relates to a BPADA type BDATHQ branched polyimide resin thin film and a preparation method thereof. The thin film comprises raw materials of BDATHQ and BPADA type linear polyamide acid resin with a mass ratio of 1: (100-800). The preparation method comprises the following steps: mixing aromatic primary diamine and a strong polar aprotic organic solvent, carrying out stirring at room temperature, carrying out cooling to 5 DEG C or below, adding BPADA, carrying out stirring, and carrying out a reaction at 5 DEG C to 10 DEG C for 1 to 6 h so as to obtain a BPADA type polyamide acid resin solution; mixing the resin solution and BDATHQ at room temperature, carrying out stirring, forming a film, carrying out heating, carrying out dehydration and thermal imidization, carrying out cooling, and carrying out demoulding. The method provided by the invention has the advantages of mild reaction conditions, simple operation, low cost, environmental friendliness, facilitation to realizing industrial large-scale production, and capability of being applied to the high-tech fields of flexible solar cells, space telescopes, large generator winding insulation, electromagnetic wire lapping electrical insulation materials, flexible copper-clad plates, etc.