Disclosed is a quantitative liquid discharge device capable of discharging liquid in a container at a preset liquid level. The device comprises a liquid discharge pipe (1), an outer sleeve (2) and a liquid level control rod (3). The liquid discharge pipe (1) is provided with a full-discharge liquid discharge port (10) and at least one internal defined-level liquid discharge port (11). Installed outside the liquid discharge pipe (1), the outer sleeve (2) is provided with external defined-level liquid discharge port (21). The wall of the liquid level control rod (3) is slidably sleeved between the wall of the liquid discharge pipe (1) and the wall of the outer sleeve (2). The liquid level control rod (3) is provided with a liquid guide port (32) passing through the wall thereof. A sliding positioning assembly is provided between the walls of the outer sleeve (2) and the liquid level control rod (3), and by means of the sliding positioning assembly, the liquid guide port (32) achieves liquid discharge at a defined liquid level, respectively between the pair of internal defined-level liquid discharge ports and the pair of external defined-level liquid discharge ports (11, 21). By operating the liquid level control rod (3) and setting the liquid level in the liquid container after discharge, the quantitative liquid discharge device can achieve liquid discharge, without specialized monitoring and control of the process of the liquid discharge, and has the advantages of quantitative liquid discharge and saving labour costs.