In view of the problem that the receiving signal of the integrated piezoelectric micro mechanical ultrasonic transducer (PMUT) has a long tail, which makes it difficult to distinguish the near-field original echo and causes a blind area in measurement, a method to identify the echo signal in the tail section is proposed in this paper.The method uses demodulated logarithmic amplifier to compress the received signal nonlinearly and carry out envelope processing to obtain the envelope curve with obvious extremum point characteristics in the trailing section. The peak value of echo is identified by the extremum point of envelope curve. Eight groups of PMUT devices with different resonant frequencies were selected to test and verify the method. The results show that the measuring blind area is reduced to around 10 cm when the farthest distance is more than 300 cm, which demontrates that the proposed method has certain effectiveness and universality.