Gas well relief line plays the key role in timely discharging high-pressure particle-laden gas flow to ensure safe test and exploitation. However, the boosting output is usually fluctuation, intehsifying the flow erosion and flow induced vibration of relief line. In this work, numerical investigation was carried out to examine the effects of fluctuation amplitude and fluctuation period of discharge capacity on the flow erosion and flow induced vibration. Unsteady Reynolds-Averaged-Navier-Stokes (URANS) equations are employed to describe the hydrodynamic characteristics of continuous phase (compressible gas), and discrete phase model (DPM) is utilized to describe the kinematics and trajectory of discrete solid particles (sand particles). The erosion rate and flow induced displacement of relief line are obtained by an empirical erosion model and a fluid-structure interaction (FSI) model, respectively. The results indicate that the flow properties, flow erosion and flow induced vibration are sensitive to the fluctuation of boosting output. Large displacement and severe erosion present in relief line with large fluctuation amplitude or small fluctuation period of discharge capacity. (C) 2017 Elsevier Ltd. All rights reserved.