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In this paper, a Petrel II autonomous underwater glider (AUG) was used to analyze underwater noise spectrogram in the South China Sea. For ocean observations, AUG has an excellent performance such as being efficient in all weather conditions, lasting for long time periods, being able to be remote controlled, which creates favorable conditions for analyzing underwater noise characteristics. In order to measure the underwater noise, a newly developed and customized underwater passive acoustic monitoring system was firstly installed on the Petrel II glider and tested in the South China Sea trial in August 2016. The observation data at a depth of 1000 meters range were taken as the research object and were used to analyze the noise levels over a long period through the method of the short-time Fourier transform. At the same time, the noise data have been compared in time to the actions of the glider during the sea trial. However, AUGs also have limitations such as undesired instrument and flow noise. By adopting the step-by-step method, these self-noise data of Petrel II glider were acquired and analyzed quantitatively, and the basic characteristics of self-noise under different working conditions are depicted. Removing the corresponding self-noise, the noise data at different depths measured by the Petrel II glider could be used to estimate underwater ambient noise levels across depth. [ABSTRACT FROM AUTHOR]