In order to non-destructively evaluate the microstructure and strengthening state of GH738 forging products during the heat treatment and brazing production cycle, the GH738 alloy is heat-treated under solution, stabilizing, ageing and braze welding treatment conditions. Metallographic and ultrasonic tests are carried out. The metallographic structure and ultrasonic characteristics are established. The mapping relationship between signal parameters is detected, and the influence mechanism of tissue changes on the changes of ultrasound signal parameters is analyzed. Results show that the effect of grain diameter on sound velocity is weak. During the hot working process, the sound velocity decreases after solution treatment, and the sound velocity continues to increase after stabilization and aging treatments. After the brazing process, the sound velocity starts to decrease and get minimum. The attenuation coefficient and non-linear coefficient change with the grain diameter. Both of them rise to the stabilization process and then slowly rise to flatten out. That means ultrasonic attenuation and non-linear coefficients can be used to characterize the grain diameter and texture discontinuity of GH738 alloy.