Two dianhydrides, namely 4,4'-oxydiphthalic dianhydride and 2,2'-Bis[4-(3,4-dicarboxyphenoxy)phenyl] propane dianhydride, and one diamine (4,4'-Diaminodiphenyl sulphone), have been used for the synthesis of a novel co-polyimide with good solubility, high visible light transparency and high thermal stability. The solubility in several solvents of polyimides with different proportion of dianhydrides has been tested, and the glass transition temperature is determined by differential scanning calorimetry. The polyimide film has been prepared and the optical transmittance is mensurated. The polyimides solubility and light transmittance improved by introducing flexible monomer, and the glass transition temperature of the polyimides is well controlled by the content of 2,2'-Bis[4-(3,4-dicarboxyphenoxy)phenyl] propane dianhydride that has the flexible isopropylidene structure.