To develop poly (lactic acid) (PLA) composites with high flame retardancy and excellent transparency is still a challenge. In this work, a phenylmaleimide bridged phosphaphenanthrene derivative (DHD) containing bisphosphaphenanthrene and phenylmaleimide groups was synthesized, and PLA composites based on DHD with excellent flame retardancy and transparency were prepared. The results showed that with the addition of just 2.5 wt% DHD, the PLA composites had a limiting oxygen index (LOI) of 28.6 % and achieved UL-94 V-0 rating. Meanwhile, the peak heat release rate of the PLA/DHD-2.5 was reduced by 7.70 % compared to pure PLA. It is worth mentioning that the PLA composites have good transparency properties. The flame retardant mechanism study indicated that the high flame retardant efficiency of DHD was attributed to the molecular synergistic effect between bisphosphophenanthrene and phenylmaleimide groups.