The effect of silty sand on the dynamic mechanism of corrosion products formed on carbon steel in a CO2 environment containing 3.5 wt% NaCl and 0.1 wt% NaHCO3 is investigated. Silty sand has a dual effect on the corrosion products structure. First, silty sand presents on the surface, and embeds in the Fe3C network. Then, silty sand delays the FeCO3 precipitation, and changes the FeCO3 crystals growth manner and structure. Silty sand decreases active surface area, but this effect is less significant than FeCO3 precipitation. Consequently, silty sand first alleviates, then promotes general corrosion rate, while always alleviates localized corrosion.