The invention provides a telescopic boom mechanism of a crane, which comprises a telescopic boom and a hoisting mechanism arranged on the telescopic boom, wherein the telescopic boom comprises n joints of suspension arms; the hoisting mechanism comprises a lifting hook, a steel wire rope for lifting the lifting hook and a winding device for taking up and paying off the steel wire rope; in the suspension arms from the first joint to the joint A, a front pulley is arranged at the front end of the first joint of the suspension arm, a rear pulley is arranged at the middle and rear part of the joint A of the suspension arm, the front pulleys and the rear pulleys are respectively arranged at the front ends and the middle and rear parts of the intermediate suspension arms, and the steel wire rope sequentially bypasses the front pulleys and the rear pulleys from the first joint of the suspension arm to the joint A of the suspension arm for constituting a movable pulley group and then extends outwards for connecting to the lifting hook, wherein the A is not less than 2 and not more than n. When the joint A of the suspension arm and the intermediate suspension arms expand and contract, the front pulleys and the rear pulleys on the suspension arms can move together with the joint of the suspension arm, thereby ensuring that the length of the steel wire rope above the lifting hook can keep unchanged, preventing the winding device from taking actions, greatly improving the expansion and contraction operation efficiency of the telescopic boom and being convenient to operate.