The invention discloses a method for determining the ground mark time of an inner detector of a pipeline, relating to the technical field of inner detection of the pipelines. The method comprises the following steps of: acquiring a friction sound signal which is generated by the friction between the inner detector and the pipe wall and meets a preset rule by an acoustic ground mark system; acquiring an envelope signal through band-pass filtering, full-wave shaping and enveloping acquiring processing; establishing a mathematical model that the amplitude of the friction sound signal of the inner detector, which is received by the ground marker, changes along with the time; substituting the vertical distance between a sensor of the ground marker and a pipeline, the operation speed of the inner detector of the pipeline within a signal time period as well as the obtained envelope signal into the established mathematical model; and acquiring the ground mark time through least square fitting. Proved by experiments, the error of the acquired ground mark time obtained through the method is little; the acquired ground mark time is more accurate and can meet the requirement of projects; and the odometer wheel error of the inner detector of the pipeline can be corrected more accurately.