A time-of-flight measurement system based on bi-echo method and digital correlation method is proposed and built.Bi-echo method is used to calibrate circuit delay of sensor and obtain reference signal for measurement.Take the maximum location of two-layer correlation function between reference signal and receiving signal as coarse location point

by linear interpolating the Hilbert transform function around this coarse location point

the zero-crossing point is acquired to be the final measurement value of time-of-flight.The calibration precision of the system can reach fs level

and the single measurement precision can reach a few ns.The system can obtain reliable and precise ultrasonic time-of-flight

and can be applied to the fields of distance

flow and wind velocity measurement.