Abstract: Usually we measure and deduct the t0 reading of concrete ultrasonic transducer by using the standard bar. But when taking the head wave amplitude as “the constant-amplitude reading” according to the testing standard, it always causes the error of t0 reading. The routine thought of operator and doctrine using of this operating procedure will certainly lead to the mistake of sonic speed miscalculation. It was showed the collect ways of deducting the t0 reading of transducer by using standard bar.