Polyamic acids (PAA) were synthesized by solution polycondensation of aromatic diamine with dianhydride and PAA were readily soluble in polar organic solvents (N-methylpyrrolidinone, N, N-dimethylacetamide and DMF). It was found that the most appropriated reaction conditions of synthesis of PAA solution were the ratio of dianhydride with diamine being 1.02:1and 3h reaction time at ambient temperature in both N-methylpyrrolidinone and N, N-dimethylacetamide polar organic solvents. PAA thin films were prepared by PAA solution spread on the glass plate and PI thin films were obtained by the casted thin films which underwent a special high-temperature (300°C, 2h) heat curing. The structures of PAA and PI films were characterized by FT-IR spectra and degree of imidization of PAA solution was indicated from IR spectra. The thermal stability was studied by thermogravimetric analysis (TGA) and the thermal behaviors were investigated by differential scanning calorimetry (DSC) in this paper. It was shown that PAA solution were imidization at 200°C mostly and PI had higher thermal stability.