Main arm telescopic mechanism and automobile crane with same

The utility model provides a main arm telescopic mechanism and an automobile crane with the same. The main arm telescopic mechanism comprises a base arm, four knuckle arms, a telescopic oil cylinder (12) and a mechanical lock (5), wherein a cylinder barrel of the telescopic oil cylinder (12) is fixed at the tail of the third knuckle arm (9); a cylinder rod of the telescopic oil cylinder is provided with a cylinder pin (14); a first cylinder pin hole (15) is arranged at the tail of the base arm (4); and a second cylinder pin hole (16) is arranged at the tail of the second knuckle arm (3). The main arm telescopic mechanism comprises a first steel rope (8), a second steel rope (10) and a third steel rope (2). The main arm telescopic mechanism optimizes the layout of the oil cylinder and the steel ropes and reduces the weight of the mechanism and the cost.