Distinguishing gas–liquid two-phase flow patterns is a fundamental issue in academic research and engineering applications. In this paper, a novel method based on temperature fluctuation is proposed for identifying the gas–liquid flow pattern. The temperature of the heated pipe wall synchronously fluctuates with the phase alternation when gas–liquid flow passes. The relationships between fluctuation parameters (intensity I, frequency f, velocity vf, and temperature difference ΔTw) and the flow characteristics of the gas–liquid flow under different flow patterns are discussed. Results show that I and vf first increase and then decrease with the increase in gas flux. In bubbly flow, I hardly changes and remains at an extremely low value that is less than 0.09%, and the churn flow has a larger vf than the slug and annular flows with a critical value of 2.2 m/s. Identification accuracy can reach 95% by coupling the fluctuation parameters.