Sound pressure is an important parameter for marine ambient noise monit oring.A laser interferometric hydrophone is designed based on Michelson interferometry to measure the offshore sound pressure of marine ambient noise.By tracking compensation method,the immunity from interference of the hydrophone is improved to some extent.Error analysis based on field data shows that the vibrating membran e is the main source of the sound pressure errors,which can be eliminated to a certain extent by appropriate vi brating membrane materials selection and optical-path optimization design.Offshore data show that hydropho ne pressure measurement is of high precision,and with a satisfactory frequency response.Comparative experiments w ith theoretical models can also verify the accuracy of the data.In coastal waters,wind noise and ship radiate noise are the main sources of marine ambient noises.Here,marine am bient noise spectra under three different wind speeds are calculated,and Kundsen curves are compared. Results show that measured data and Kundsen curve fitting are better both in trend and value,and the static noise source model is prevalence of a difference of about 20dB.In addition,the measurement of vessel radiation noise is mainly concentrated in frequency range of 350－500Hz.