Maleimide polymers are used as potentially excellent optical materials, but if these polymers cannot be degraded, them will bring environmental pollution and other problems. Based on our previous work about maleimide polymer with phenyl selenide in the side of double bond, gel permeation chromatography (GPC), ultraviolet-visible (UV-vis) spectrum and electron spin resonance (ESR) spectroscopy were utilized to study the photoresponse and photodegradation behaviors of these polymers. The results show when the prepared polymers are irradiated 1 h by UV light, their number molecular weight (Mn) will reduce to be half. With the extension of irradiation time, the molecular weight of these polymers will reduce in continue. However, selenide compound is added into the maleimide polymer without phenyl selenide group, and it will not bring light degradation after UV irradiation. In addition, it is found that similar structure maleimide polymer cannot be degraded by UV light after changing selenide stricture to thioether stricture.