Cationic surfactants can change the surface properties of rocks and could be used to reduce the rate of acid-rock reaction to ensure that the acid was pushed deeply into the reservoir. In order to reveal the effect of the carbon chain length of the cationic surfactant on the retarding performance，in this paper，the critical micelle concentrations of tetradecyltrimethyl ammonium chloride，hexadecyltrimethyl ammonium chloride，octadecyltrimethyl ammonium chloride and dodecyltrimethyl ammonium chloride（C_nTAC，n=14，16，18，22）were determined by surface tensiometer and conductivity meter. Atomic force microscope was used to observe the adsorption patterns of C_nTAC on the rock surface. The solid/gas/liquid three-phase contact angle method was used to study the ability of C_nTAC changing the surface wettability of calcite. Finally，the static acid-rock reaction rate was tested. The experimental results showed that with the increase of the carbon chain length，the c_cmc of the C_nTAC decreased obviously，the adsorption of C_nTAC on calcite surface was mainly monolayer adsorption；C_nTAC could reversed wettability of hydrophilic solid surface to lipophilicity，with the increase of carbon chain length，the thickness of adsorbed layer of calcite treated by C_nTAC decreased and the hydrophobicity of calcite increased. C_nTAC could effectively reduce the acid rock reaction rate and the C₁₄TAC had the best retarding properties，the retardance rate was 69.70%，with the increase of carbon chain length，the retardation performance of C_nTAC became worse，and the surface morphology of calcite etching tended to be inhomogeneous.