The invention discloses a method for detecting and warning moving speed of a probe of a portable flaw detector. Steel plate bottom wave waveform transmitted by the probe is received by the portable flaw detector and is displayed on a screen; a wave loss warning gate is additionally arranged on the waveform, the wave loss gate is not closed when the steel plate bottom wave waveform is stable, ultrasonic wave penetrates through a steel plate to perform detection operation, and missing detection condition is avoided; due to the fact that the probe moving speed is too high, the waveform is not stable and the bottom wave is reduced or disappears; and the wave loss gate is newly increased to warn and makes prompt for limiting the probe moving speed. The method has the characteristics of increasing the probe moving speed, increasing flow detection yield, reducing missing detection probability of nondestruction detection and increasing the detection rate.