The invention discloses an ultrasonic detection and diagnosis method for hydrogen damages on the water-cooling wall pipe of a boiler. The ultrasonic detection and diagnosis method comprises the following steps of: selecting a pipeline having the same outer diameter as the water-cooling wall pipe needing to be detected and diagnosed, of the boiler, as a detected pipe sample; using an ultrasonic detection instrument with a pulse-reflection type transverse wave angle probe, and causing the probe to be in close contact with the detection surface of the detected pipe sample; preparing a DL-1 type special test block according to the material of the water-cooling wall pipe of the boiler, and calibrating the performances of the ultrasonic detection instrument and the transverse wave angle probe; drawing a distance-amplitude curve by virtue of the DL-1 type special test block; performing ultrasonic detection for transverse defects on the water-cooling wall pipe needing to be detected and diagnosed, of the boiler; analysing the waveform characteristics of ultrasonic wave and the typical waveform characteristics of hydrogen damages, if the diagnosed result is the hydrogen damages, then using the equivalent value of the maximum echo amplitude in a detection echo for evaluating the relative degree of the hydrogen damages in the defect area of the detected pipe sample. The method is a reliable, convenient and rapid ultrasonic detection and diagnosis method.