Abstract: A method that uses a random surface to improve measurements of the radiated sound power in a non-anechoic tank is proposed. Based on the finite element method, the feasibility of improving sound power measurements at low frequencies by random surface in a non-anechoic pool is analyzed. The sound power of a spherical source is measured in a non-anechoic tank with a size of 1.2 m × 1.0 m × 0.8 m. Experimental results show that in contrast to a tank with a steady surface, once a random surface is generated using a water pump, the diffusion is significantly improved: (1) the Schroeder frequency is decreased from 10015 Hz to 8370 Hz, indicating the range of measurement is extended to lower frequencies; (2) the frequency response curves measured by spatially averaging techniques have smaller fluctuation and is closer to free-field value, that is, the accuracy of measurement is significantly improved. The proposed method contributes to obtaining more accurate narrowband measurements of underwater target acoustic characteristics in underwater environment environments.