A time-of-flight generating circuit, coupled to a first transducer and a second transducer, wherein there is a distance greater than zero between the first transducer and the second transducer, and the first transducer and the second transducer are arranged in a pipeline filled with fluid, comprising: a transmitter, coupled to the first transducer; a receiver, coupled to the second transducer; a signal generating circuit, configured to, under a first ambient temperature, generate a first signal (S1 2) to the transmitter to cause the first transducer transmit a first transducer signal (TS1 2), wherein the first transducer signal (TS1 2) is received by the second transducer and the receiver generates a reference signal (RS 2) to the signal generating circuit; and, under a second ambient temperature, generate a second signal (S2 2) to the transmitter to cause the first transducer transmit a second transducer signal (TS2 2), wherein the second transducer signal (TS2 2) is received by the second transducer and the receiver generates an input signal (IN 2) to the signal generating circuit; a correlation circuit, configured to receive the input signal (IN 2) and a synthesized signal (SS 2) to perform a correlation operation to generate a correlation signal (COR 2); a measuring circuit, configured to generate a measurement signal (MS 2) according to the correlation signal (COR 2), wherein the measurement signal (MS 2) indicates a phase difference between the input signal (IN 2) and the reference signal (RS 2), and the measurement signal (MS 2) includes a first measurement signal (MS1 2) and a second measurement signal (MS2 2), wherein the first measurement signal (MS1 2) is configured to indicate a phase compensation of the input signal (IN 2) and the reference signal (RS 2), and the second measurement signal (MS2 2) is configured to indicate a phase offset of the first transducer and the second transducer; a compensation circuit, coupled to the measuring circuit and configured to perform a compensation operation on the input signal (IN 2) to generate a compensation signal (CS 2) according to the first measurement signal (MS1 2); a synthesis circuit, coupled to the compensation circuit and the signal generating circuit and configured to synthesize the reference signal (RS 2) and the compensation signal (CS 2) by using a specific ratio to generate the synthesized signal (SS 2) and output the synthesized signal (SS 2) to the correlation circuit; and a transformation circuit, configured to transform the measurement signal (MS 2) from a frequency domain to a time domain to generate a TOF difference signal (TOF 2), wherein the TOF difference signal (TOF 2) is configured to indicate a difference of flight times between the first transducer and the second transducer. a transmitter, coupled to the first transducer; a receiver, coupled to the second transducer; a signal generating circuit, configured to, under a first ambient temperature, generate a first signal (S1 2) to the transmitter to cause the first transducer transmit a first transducer signal (TS1 2), wherein the first transducer signal (TS1 2) is received by the second transducer and the receiver generates a reference signal (RS 2) to the signal generating circuit; and, under a second ambient temperature, generate a second signal (S2 2) to the transmitter to cause the first transducer transmit a second transducer signal (TS2 2), wherein the second transducer signal (TS2 2) is received by the second transducer and the receiver generates an input signal (IN 2) to the signal generating circuit; a correlation circuit, configured to receive the input signal (IN 2) and a synthesized signal (SS 2) to perform a correlation operation to generate a correlation signal (COR 2); a measuring circuit, configured to generate a measurement signal (MS 2) according to the correlation signal (COR 2), wherein the measurement signal (MS 2) indicates a phase difference between the input signal (IN 2) and the reference signal (RS 2), and the measurement signal (MS 2) includes a first measurement signal (MS1 2) and a second measurement signal (MS2 2), wherein the first measurement signal (MS1 2) is configured to indicate a phase compensation of the input signal (IN 2) and the reference signal (RS 2), and the second measurement signal (MS2 2) is configured to indicate a phase offset of the first transducer and the second transducer; a compensation circuit, coupled to the measuring circuit and configured to perform a compensation operation on the input signal (IN 2) to generate a compensation signal (CS 2) according to the first measurement signal (MS1 2); a synthesis circuit, coupled to the compensation circuit and the signal generating circuit and configured to synthesize the reference signal (RS 2) and the compensation signal (CS 2) by using a specific ratio to generate the synthesized signal (SS 2) and output the synthesized signal (SS 2) to the correlation circuit; and a transformation circuit, configured to transform the measurement signal (MS 2) from a frequency domain to a time domain to generate a TOF difference signal (TOF 2), wherein the TOF difference signal (TOF 2) is configured to indicate a difference of flight times between the first transducer and the second transducer.