The invention discloses a thunder early warning system and early warning method suitable for power transmission line construction operation. The system comprises a thunder early warning information processing platform, a thunder early warning information issuing platform and a thunder early warning information issuing terminal. The thunder early warning information processing platform comprises an early warning original database, a geographic information database and an early warning information processing center, wherein the communication ends of the early warning original database and the geographic information database are both connected with the communication end of the early warning information processing center, and the signal output end of the early warning information processing center is connected with the signal input end of the thunder early warning information issuing terminal through the thunder early warning information issuing platform. According to the invention, multiple monitoring data is employed for integrated thunder early warning so that the thunder early warning precision is quite high, and the restrictions of thunder early warning regions, brought by the monitoring scope of an atmosphere electric field instrument and a lightning interferometer in the prior art, are solved.