Photosensitive copolysiloxaneimides were prepared by adding a photosensitive monomer such as hydroxyethylacrylate (HEA) to copolyisoimides, which were synthesized by the copolycondensation of pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride with oxydianiline, and bis(p-aminophenoxy)dimethylsiloxane. The forming process of isoimide rings caused by the reaction of polyamic acid with dicyclohexylcarbodiimide and the disappearance process of isoimide rings caused by the reaction of copolyisoimide with HEA were monitored in situ by infrared approach. A series of photosensitive copolysiloxaneimides films were prepared, and the desired structure-properties relationships about inherent viscosities, thermal expansion coefficient, thermal stability and glass transition temperature, dielectric constants, moisture absorption, and photosensitivity were also discussed.