In order to study the effects of silica sand on synergistic erosion caused by cavitation, abrasion, and corrosion, vibratory experiments were conducted on ASTM 1045 carbon steel specimens subjected to six particle sizes (0.01–0.1 mm) mixed in nine concentrations (6–300 kg/m3) with tap water or with six concentrations of NaCl (0.5–15%). The experimental results indicate that sand particles larger than 0.04 mm at concentrations of 30–150 kg/m3 increasingly aggravated synergistic erosion with increasing sand particle size and concentration. The difference was observed for sand particles smaller than 0.04 mm: these sands inhibited cavitation erosion at concentrations of 30–300 kg/m3, but aggravated erosion at concentrations of 6–30 kg/m3; the maximum erosion occurred at a concentration of 12 kg/m3. As the concentration of NaCl increased, the erosion due to cavitation and corrosion increased sharply before growing stable above a NaCl concentration of 3.5%. The synergistic erosion caused by cavitation, abrasion, and corrosion was more severe than the erosion in tap water or cavitation-corrosion in a 3.5% NaCl solution, demonstrating that sand has an aggravated effect on synergistic erosion.