Seawater density, as a critical parameter governing oceanic dynamic processes, demands precise measurement for advancing marine environmental studies. While optical sensors offer inherent advantages in density measurement through refractive index detection—including electromagnetic immunity, high sensitivity, and provide response to non-ionic solutes—their measurement stability in dynamic marine environments remains compromised by fluid flow interference. This study addresses this challenge by proposing a novel anti-flow structural design to improve measurement consistency under hydrodynamic disturbances. Traditional conductivity-temperature-depth (CTD) sensors, though widely utilized, suffer from inherent limitations. Their indirect density calculation via TEOS-10 equations exhibits reduced sensitivity to non-ionic components and necessitates energy-intensive pumping systems that introduce mechanical vibrations. Our objective focuses on developing a flow-immune optical sensor that eliminates auxiliary pumps, minimizes turbulence-induced errors, and validates its performance through systematic laboratory and field experiments. By optimizing fluid exchange patterns within the sensing cavity, this design aims to achieve high-precision density measurements under varying flow conditions, thereby enhancing the reliability of optical sensing technology in practical oceanographic applications.This study developed a seawater density sensing system based on spectral interferometry. The sensing probe features two parallel sapphire optical windows spaced 10 mm apart, allowing seawater to flow freely through the measurement cavity. A pump-free anti-current design was implemented through hydrodynamic-optimized channel geometry: V-shaped inlet channels with a 45° inclination angle paired with linear drainage grooves (Fig.2) enhance unidirectional flow efficiency. Variations in refractive index were detected via wavelength shifts of interference extrema using a high-resolution spectrometer.In the seawater flow velocity simulation device, the measurement environment was simulated with seawater flow velocity ranging from 0.01 m/s to 2 m/s. Under these conditions, the interference fringe contrast recorded by the optical density sensor remained above 0.8, and the fluctuation in density measurements was consistently within the order of 10^-3 kg/m³. Subsequently, a profiling test conducted at a maximum depth of approximately 3600 meters to evaluate, the consistency between the measurements of optical density sensor and the CTD sensor. The density difference between the two sensors remained within ±4×10^-3 kg/m³, confirming the effectiveness of the anti-flow design in complex oceanic environments.This study successfully demonstrates the effectiveness of an anti-flow optimized optical sensor for measuring seawater density in dynamic environments. Laboratory tests conducted under controlled flow conditions (≤2 m/s) confirmed exceptional stability, with standard deviations in density measurement maintained below 1×10^-3 kg/m³. Field profiling experiments revealed strong consistency between optical and CTD sensor measurements, with a mean absolute density error of 2.4×10^-3 kg/m³. The anti-current design eliminates the need for pumping systems while improving fluid exchange efficiency, effectively suppressing turbulence-induced signal fluctuations through hydrodynamically optimized channel geometry. These findings establish the sensor's capability for high-resolution density monitoring in complex marine environments, offering a potential supplement to CTD sensors, and advancing real-time monitoring of fine-scale oceanic processes.