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.