The invention discloses a longitudinal wave normal probe full-beam-path non-blind-area flaw detecting method. The method includes the steps of firstly, arranging a longitudinal wave normal probe on the surface of a to-be-detected workpiece; secondly, setting time baseline conditions so that secondary bottom waves can be adjusted to a position in a certain ratio range of the overall length of a scanning line of an oscilloscope screen with the thickness of the to-be-detected workpiece as the standard; thirdly, setting sensitivity conditions so that sensitivity adjustment can be conducted on the longitudinal wave normal probe according to parameters corresponding to the double value of the thickness of the to-be-detected workpiece; fourthly, sending ultrasonic beams from the longitudinal wave normal probe to detect flaws of the to-be-detected workpiece; fifthly, judging whether flaws exist in the to-be-detected workpiece or not and calculating corresponding flaw information on the basis of the thickness value of the to-be-detected workpiece and the position information of primary bottom waves, secondary bottom waves and flaw echoes in reflected echo signals received by the longitudinal wave normal probe on the scanning line of the oscilloscope screen. The flaws are detected on the basis of the secondary bottom waves, and the effect of full-beam-path non-blind-area flaw detecting is achieved.