The invention discloses a coiled tubing falling-prevention device and a usage method thereof. The coiled tubing falling-prevention device comprises a spear-shaped central rod, a grooving slip and a limiting prevention cylinder which are sequentially arranged from inside to outside in a sleeved mode. The inner wall of the limiting prevention cylinder sequentially and inward sinks from top to bottom step by step to form a first annular step and a second annular step which are in shapes of steps, the top end face of the grooving slip abuts against the lower end face of the first annular step, an outer thread is arranged on the outer wall of the spear-shaped central rod, a connecting outer thread is arranged on the inner wall of the first annular step of the limiting prevention cylinder, and the grooving slip is limited by adjusting the limiting prevention cylinder relative to the position at the thread connecting position on the spear-shaped central rod. A falling-prevention function during coiled tubing fishing can be played by using the coiled tubing falling-prevention device. When a dangerous overflow case appears at a well opening, blowout prevention short section matched with the device is rapidly installed in time, and the blowout prevention problem of a coiled tubing inner cavity and a small annulus between the coiled tubing and an oil pipe can be also solved.