Specimens of the 7 N01 aluminum alloy with different grain sizes were prepared by means of heat treatment in this paper in order to analysis the grain size qualitatively. The stress constant K of the specimens after heat treatment was calibrated by uniaxial tensile calibration test. The results showed that the stress constant K increased with the material grain size increasing. The author built the ultrasonic testing platform in this paper. The nominal t,0, of the specimens was get based on the cross correlation calculation between reference waveform and capture waveform. The material t,0, was also positively associated with the grain size. The relationships between K,t,0, and voltage attenuation were established in this paper. Then, the constitutive equation of K,t,0, and voltage attenuation was fitted. Therefore,the modified model between the attenuation of LCR wave and the propagation time was established in this paper,and the change of K and t,0, were represented by the voltage amplitude.