The present invention relates to a dynamic automatic liquid-level detector for an oil well and belongs to the oil field automatic detecting technical field; the dynamic automatic liquid-level detectorconsists of a test tube (1), a sensor (2), an electromagnetic valve (3), a container (4), an electromagnetic valve (5), an electronic unit (6), a sound velocity determine tube (7), and a blind-terminal(8); the test tube (1), the solenoid valve (5) and the container are connected in series way one by one, which easily triggers and controls the width and the intensity of a pulse sound source; the container is connected with the test tube (1) through the electromagnetic valve (3), and communicated with atmosphere or connected with external low-voltage pipes through the electromagnetic valve (5);a special thin and long blind pipe is arranged beside the three-way sensor at the middle of the test tube to test the real velocity of sound; the open and the close of the electromagnetic valves (3)and (5) are controlled by the electronic unit (6) which collects the signals from the sensor (2) and calculates the depth of the liquid, and then displays and carries out a further transfer of the data; the dynamic automatic liquid-level detector has the advantages that the dynamic automatic liquid-level detector can spring the sound source automatically; and can control the pulse and the width of the sound source; and also can detect the velocity of the sound quickly and correctly without being effected by the factors of casing pressure, temperature, the amount of liquid contained in gas.