The invention discloses a wearable upper limb exoskeleton power-assisting device. The wearable upper limb exoskeleton power-assisting device comprises mechanical arm devices, a supporting device and gripping devices, wherein each mechanical arm device comprises a pedestal, a power assembly and an arm assembly; each arm assembly 13 is a main holding part of each mechanical arm device 1; motion of each arm assembly 13 is realized by each power assembly 12; each power assembly 12 drives the corresponding arm assembly 13 to perform space motion for feeding a hand to any point within a space motion range. Through the unique mechanical structure design, free extension of the arms is realized, so that the arms have a state of relaxing and stretching and a state of lifting forearms, and are freely transited between the two states. The wearable upper limb exoskeleton power-assisting device is reasonable in structure, is relatively high in practical value, can improve ability of people, can realize carrying heavy objects easily, and relieves working strength of a worker.