The most common one in the flat wrecker is the one-pull-two wrecker truck, which can manage two trouble vehicles at a time. Although the price is more economical, the vehicle does not have the lifting ability, for the trouble car which slided out of the road, it has to ask for support from other wreckers or cranes, thus it would take a longer time. In addition, as the support arm of the flatbed wrecker truck is limited by the structure, when it is leveled, it cannot be lowered to the ground completely, just can be lowered to an negative angle for arm extension to lift the trouble vehicle. In this way, for some trouble vehicles with lower chassis, it may easy to hit the bumper, causing secondary damage to the broken vehicle. At this time, the tow crane joint vehicle can be used to complete the trailer perfectly.