Ultrasonic ranging is the most common ranging technology with high cost performance. However, the ranging error is often caused by signal shaping in common ultrasonic echo ranging mainly due to the loss of starting period and the difference of reflected signal amplitude, which makes the measured signal flight time exceed the starting time of received signal. The dual phase detection method proposed in this paper transmits a group of critical modulation signals of 64 cycle carrier and 2 cycle modulation signals, timing starts at the same time, stops timing when the amplitude of the received signal exceeds a specific threshold, then detects the phase of the signal at the threshold point, obtains the starting time point of the received signal, and then uses the carrier phase correction method to eliminate the error caused by signal shaping to obtain the distance measurement result. Through the simulation test and experimental test, the results show that the actual measurement accuracy is almost not affected by the noise and the amplitude of the reflected signal. In the range of 50~200 mm, the standard deviation of the two-phase ranging device is less than 1 mm, and the ranging accuracy is effectively improved.