Objective To survey the fatty acids and methyl mercury (MeHg) of marine fish from coastal areas of Guangdong Province and conduct risk-benefit assessment of neurodevelopmental effect, providing scientific basis for dietary instruction of marine fish from Guangdong Province. Methods The fatty acids and MeHg contents were detected in 20 species of marine fish samples collected from coastal areas of Guangdong Province. A quantitative risk-benefit assessment model with a measured value of intelligence quotient(IQ) points, proposed by Food and Agriculture Organization/World Health Organization(FAO/WHO), was performed to assess the net neurodevelopmental effect. Results The average content of total lipids for 20 species of marine fish ranged from 0.73 to 19.95 g/100 g. The content of ploy unsaturated fatty acid (PUFA) ranged from 0.18 to 5.82 g/100 g, the n-3 PUFA ranged from 135.69 to 2 232.74 mg/100 g, the docosahexaenoic acid(DHA) ranged from 73.61 to 1 334.00 mg/100 g, and eicosapentaenoic acid(EPA) varied between 43.76 and 945.67 mg/100 g. The MeHg content in all the fish samples did not exceed the GB 2762-2017 China National Food Safety Standard in this study. Three types of marine fish consumption were used in modeling. It was calculated by the mean intake(100 g/week), P97.5 intake(830 g/week)among Guangdong residents and recommended intake of aquatic products (280 g/week) for the consumption level of marine fish, respectively, and the corresponding net IQ point improvements were 0.5-5.7,3.8-5.6 and 1.3-5.7. Among these fish species, only human exposure to MeHg via consumption of Muraenesoxcinereus Trichiuruslepturus at the extreme consumption level of 830 g/week exceeded the provisional weekly intake tolerance(PTWI, 1.6 μg/kg BW). Conclusion According to the recommended intake of Chinese dietary guidelines, intake of marine fish widespread consumed in coastal areas of Guangdong Province could bring positive neurodevelopmental effects to newborns or infants, while the consumption rate should be lower for fishes with high content of MeHg (such as Muraenesoxcinereus).