An automatically-cleanable thickening performance evaluation instrument for drilling LCMs includes a cleaning device, a kettle body, a thickening motor, a heating component, a test ending component, a top cover, and a bottom cover, where upper and lower ends of the kettle body are both opened; the kettle body is arranged in a third bearing inner race, a third bearing outer race is connected to a first limb, and the first limb is configured to limit a position of the kettle body; and the kettle body is detachably connected to the thickening motor and driven by the thickening motor to rotate. The instrument can realize electric heating and air pressurization to simulate the underground environment, and the kettle body can be completely sealed, such that a measured thickening time is close to an actual thickening time. Moreover, the instrument can be automatically cleaned at the end of a test.