The harm assessment and responsibility of marine mineral oil pollution require the content of mineral oil to be obtained by real-time online monitoring In the present paper, the method of online monitoring of the oil content in water is presented, a creative technology based on optical scattering theory was proposed. Firstly the particle distribution of oil drops was scanned by Marvin laser particle meter, then with the help of the scattering signal, the crude, diesel of different concentrations from 0 to 30 mg·L-1 was measured in experiment, the linearity is more than 0.99.This paper presents a feasible setup for the online monitoring of the content of mineral oil.