The failure behavior of red phosphorus flame retardant electrical connectors was investigated by their thermal degradation, changes of surface morphology and elements under an accelerating environmental experiment. The results showed that the nylon electrical connector degraded and cracks were generated on the surface. The temperature of maximum weight loss rate was advanced in the thermogravimetric analysis and the third weight loss peaks appeared after 28 days. The relative atomic content of O and P increased from 0 day to 28 days. The chemical environment of C changed. Partially, C–C bonds broke and became C–O bonds. The release of phosphine increased and this further oxidized to an acid with PO and P–O groups in a warm and humid environment.