Annular liquid level continuous monitoring device and monitoring method for well drilling

The invention discloses an annular liquid level continuous monitoring device for well drilling, which belongs to the technical field of shaft monitoring, and comprises a rotary blowout preventer, a grouting ball valve, a three-way joint, a liquid level monitoring ball valve, a sound wave type continuous monitor, a grouting pump, a control system and an MPD pressure control system, and the rotary blowout preventer, the grouting ball valve, the three-way joint and the grouting pump are fixedly connected in sequence; the sound wave type continuous monitor is connected with the three-way connector through the liquid level monitoring ball valve, and the control system is connected with the MPD pressure control system, the sound wave type continuous monitor, the grouting ball valve, the liquid level monitoring ball valve and the grouting pump. The invention further discloses a device-based method. Automatic monitoring of the annular liquid level and automatic slurry pouring in the whole process can be achieved thro