This work first investigated the detection of slags, slag pool liquid level, and slag accumulation height in laboratory scale based on acoustic emission (AE) detection, and further tried the feasibility of thismethod in an industrial scale coal gasifier. Results show that the energy and variance of acoustic signals can realize the accurate detection of large slag (criterion: E > 1.5E(0), S > 1.2S(0)), and the average relative error is only 0.28%. The acoustic energy in the frequency range of 20-40 kHz is defined as the characteristic energy, which can realize the accurate detection of slag accumulation height and slag pool liquid level, and the average relative error is only 3.94%. Furthermore, AE detection also realize accurate detection of large slag in an industrial scale gasifier and the acoustic signals at slag screen can be used to realize the early warning of the slag collapse (5 h earlier). (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.