Fly ash air-entrained concrete specimens were tested in 3.5% NaCl solution with rapid freeze-thaw cycles.The relative dynamic modulus of elasticity and frost damaged layer thickness of concrete specimens were measured by the ultrasonic testing technology, and also the static modulus of elasticity was measured.The results showed the development process of internal cracks in concrete due to salt frost damage by microscopic observation with SEM.A certain correlation between the static modulus of elasticity and the relative dynamic modulus of elasticity can be acquired but are not in line with the calculated values by standard was carried out.The elastic characteristics development trend of reinforced concrete specimens was roughly the same as that of concrete specimens without rebar as function of number of freeze-thaw cycles.However divergences existed due to their different heat capacity, which should be important to the salt frost durability assessmen of reinforced concrete structure.