Abstract: This study takes a three-strand twisted rope with a nominal diameter of 40 mm (equal strand diameter) as the prototype. Based on the mathematical equations of the cross-sectional geometry of three-strand ropes, a prototype rope (labeled 40-40) and four variant rope models with modified strand diameters were constructed. The four variant ropes were created by replacing the original strands of the prototype with strands from three-strand ropes of nominal diameters 48, 44, 36, and 32 mm, labeled as 40-48, 40-44, 40-36, and 40-32, respectively. Physical rope models were fabricated via 3D printing, and the effects of strand diameter variations on hydrodynamic coefficients and flow field characteristics were investigated through flume experiments and numerical simulations within a Reynolds number range of 7.96×10³ to 5.57×10⁴. The results revealed that: (1) The drag coefficients of all ropes exhibited minimal variation with increasing Reynolds number. (2) The drag coefficient decreased with reduced strand diameter, while the lateral force coefficient remained relatively stable. (3) Compared to the prototype (40-40), the average drag coefficients of 40-32 and 40-36 decreased by 7.06% and 4.49%, respectively, whereas those of 40-44 and 40-48 increased by 2.22% and 5.51%, respectively. (4) The high-velocity zones around the ropes and the areas of positive/negative pressure on the rope surfaces diminished as strand diameter decreased, accompanied by weakened downstream turbulence, leading to reduced pressure difference resistance and lower drag coefficients. This study demonstrates that reducing strand diameter effectively decreases rope resistance and mitigates downstream turbulence. The findings provide valuable insights for hydrodynamic research on fishing gear and innovative design of rope-based materials in fisheries engineering.