Fiber-reinforced composites，renowned for their high specific strength，high specific modulus，exceptional fatigue resistance，and outstanding corrosion resistance，are extensively utilized across the aerospace，transportation，and energy industries. Nevertheless，under severe service conditions，the latent progression of internal damage can precipitate sudden failure，underscoring the pressing need for effective structural health monitoring （SHM） technologies. This review comprehensively summarizes the latest advancements in this field，conducting a systematic analysis of the principles，performance merits，and principal limitations of both offline nondestructive testing methods （encompassing ultrasound，X-ray/CT，infrared thermography，and acoustic emission） and online monitoring techniques （including surface-mounted strain gauges，piezoelectric and fiber-optic sensors，as well as embedded optical fiber，resistive，and piezoelectric sensors）. Comparative analysis reveals that offline techniques boast high accuracy but are devoid of real-time capability，while online techniques facilitate dynamic monitoring yet are hampered by limited penetration depth and signal interpretation capabilities. Finally，the paper delineates key avenues for future development，such as the co-design of sensors and structures，multifunctional damage sensing，and intelligent signal processing for pattern recognition and predictive maintenance，offering a valuable reference for the intelligent monitoring of composites under complex service conditions.