Abstract: The transportation and treatment systems of traditional oil fields have large footprint and low efficiency, while the oil-water separation technology of horizontal flow grid tubes is used to transform, exploring energy savings and consumption reduction. The separation law of oil-water-sludge in horizontal grid tubes was studied by combining Fluent software simulation with indoor and field experiments. The numerical simulation results showed that the longer the tube length, the smaller the fluid flow rate, and the better the oil-water separation effect. The inlet oil content increased, and the effluent increased. The oil concentration at the inlet of the six-meter gird tube should be controlled within 0.1%. The results of laboratory and field experiments were basically consistent with the results of numerical simulation, which confirmed the oil-water-sludge separation law explained by numerical simulation. Field experiments have shown that when the inlet flow rate varied between 0.02 m/s to 0.05 m/s, and the inlet oil content varied between 590 mg/L to 2710 mg/L, the effluent oil content was 63 mg/L to 86 mg/L and the suspended solids content was 86 mg/L to 145 mg/L. The grid tube has a stable removal effect on oil and suspended solids, indicating strong resistance to water quality fluctuations. It occupies a small area and has low investment and operating cost.