Abstract: Hydrogen energy has the advantages of wide source, clean and carbon-free. With the wide application of hydrogen energy, hydrogen energy storage and transportation has gradually become a research hotspot. At present, the carbon fiber reinforced resin matrix composite material gas cylinder vigorously developed by the country has been widely used in the field of hydrogen energy storage and transportation, but the gas cylinder is prone to fiber breakage and scratches during use and transportation, which seriously affects the safety of use, so it is urgent to develop the carbon fiber reinforced resin matrix composite material gas cylinder online monitoring technology. In order to solve the problem that fiber fracture and scratch defects of composite material gas cylinders will expand during long-term and multiple filling and venting, an online monitoring method using electromagnetic acoustic transducer (EMAT) was adopted. Combined with the 90TJ3-140 MPa hydraulic pressure fatigue system, the influence of fiber damage on the amplitude of guided wave was analyzed by ultrasonic guided wave reflection method and ultrasonic guided wave transmission method, and the variation of guided wave signal characteristics of gas cylinders with fiber damage under different fatigue conditions was studied. The results show that fiber damage can reduce the amplitude of transmission wave, and the amplitude reduction is determined by the degree of fiber damage. With the increase of the pressure inside the cylinder, the sound velocity and center frequency of ultrasonic guided wave decrease gradually. For cracks with length 20 mm, width 0.5 mm and depth 1 mm, the amplitude of the defect wave increases first and then decreases. After 110 MPa and 80 cycles, the amplitude of the defect wave decreases from 19.33 mV to 8.02 mV, the sound velocity decreases by 6.6%, and the center frequency decreases from 0.24 MHz to 0.17 MHz, the fibers are completely layered. For cracks with a length of 20 mm, a width of 0.5 mm and a depth of 0.5 mm, when the internal pressure of the cylinder increases from 0 MPa to 105 MPa, the direct wave amplitude decreases from 80.17 mV to 20.08 mV, which decreases by 75%. The electromagnetic ultrasonic technology can effectively solve the difficult problem of on-line monitoring of carbon fiber reinforced resin matrix composite material gas cylinder.