Effects of NaCl-MgCl₂ compounded deicing salt on the ice-formation pressure and the critical saturation degree of salt solutions， and on the salt-frost scaling and the degree of saturation of concrete were investigated. The mechanism of reducing the salt-frost scaling of concrete by the above compounded deicing salt was revealed. The results show that adding MgCl₂ into NaCl deicing salt effectively reduces the salt-frost scaling of concrete caused by salt solutions. With the increase of MgCl₂ content in the compounded deicing salt， the ice-formation pressure of salt solution is less effected， but the critical saturation degree of salt solution is significantly increased， and the degree of saturation of concrete adding compounded deicing salt and its increasing rate is significantly reduced during freezing-thawing cycles.