The invention discloses a balance device for transmission of a numerical control machine. The balance device for transmission of the numerical control machine comprises a balance device body, inner box fixators, an adjusting ring and an inner box. The inner box fixators are installed inside the balance device body. One outer fixator is installed outside each inner box fixator. The inner box is installed inside the inner box fixators. The adjusting ring is installed inside the inner box. Spring fixing troughs are installed on the top of the adjusting ring. Springs are installed inside the spring fixing troughs. A cushion pad is installed at the bottom of the adjusting ring. Bearing fixing troughs are installed outside the cushion pad. An anti-drop cover is installed at the bottom of the balance device body. A bottom connection device is installed above the anti-drop cover. A stress device is installed above the balance device body. According to the balance device for transmission of the numerical control machine, because the fixators are installed on the outer side of the inner box, it can be guaranteed that the internal structure will not change when the balance device is in use; and because the anti-drop cover is installed at the bottom of the balance device, parts can be prevented from dropping off.