Abstract Basin‐type insulator often has small cracks due to stress concentration. The current method cannot accurately reflect the stress condition of the insulator to find the stress concentration areas. To solve these problems, a method for detecting two‐dimensional plane stress (δ1 and δ2) within different depth ranges in a basin‐type insulator is proposed based on critically refracted longitudinal (LCR) wave. First, the acoustoelastic equation characterising the relationship between the variation of LCR wave propagation time and the plane stress was derived. Next, the propagation characteristics of LCR wave in epoxy resin samples were investigated. Then, the stress distribution within different depth ranges of the insulator subjected to hydraulic load was measured using the proposed method, including direction (θ), δ1 and δ2. The results show that the magnitude of the stress alone cannot accurately characterise the stress state. Points with equal distances to the centre have similar stress magnitudes, but their directions are not the same. With increasing depth, θ remains essentially unchanged at the same location, while δ1 and δ2 decrease, and the rate of decrease varies at different locations. Comparing the measured and simulated data, the results showed that they were in good agreement, and the maximum errors of stress value and θ were 0.69 MPa and 2.97°, respectively, which confirmed the feasibility and accuracy of the stress detection in the proposed method.
