The invention relates to the field of pier protection devices, in particular to a protection device for a mountain pier against impact of rolling stone and debris flow. The device comprises an impactprevention plate, wherein the outer surface of the impact prevention plate is fixedly connected with a shunt plate; the middle part of the impact prevention plate is provided with a circular arc shuntblock; the inner surface of the impact prevention plate is fixedly connected with a plurality of shock absorbing springs; the tail end of the impact prevention plate is fixedly connected with a plurality of protection plates; and one end, away from the impact prevention plate, of each shock absorbing springs is fixedly connected with an impact prevention inner plate. The invention has the advantages that the purpose of changing the motion track of the rolling stones is achieved through the shock absorbing spring, the impact preventing plate and the impact preventing inner plate; when the rolling stones fall on the hillside, a part of the rolling stones impact the impact preventing plate, the impact preventing plate bears the impact of the rolling stones; the shock absorbing spring ejectsthe rolling stones, the motion track of the rolling stones is changed, and the effect of preventing the rolling stones is achieved; and the shock absorbing spring evenly disperses the impact force ofthe rolling stones, so that the impact preventing plate bears the impact force as a whole instead of a certain point on the impact preventing plate.