The invention discloses a probe module for online flaw detection of trains. The probe module comprises a module bottom plate, a first side plate, a second side plate, a probe bottom plate, a module cover plate, a probe and a water spraying device, wherein the first side plate and the second side plate are arranged on the module bottom plate; the two ends of the probe bottom plate are connected with the first side plate and the second side plate respectively; the module cover plate is located at the tops of the first side plate and the second side plate; the probe penetrates through the module cover plate; the water spraying device is used for spraying coupling water; the probe bottom plate is located at the bottom of the module cover plate and the probe is connected with the probe bottom plate through a spring; the module cover plate is clamped with the first side plate; and the module cover plate and the second side plate are clamped with the water spraying device. According to the probe module for the online flaw detection of the trains, disclosed by the invention, the structure of the whole probe module is effectively simplified so that assembling is simplified; meanwhile, the module cover plate is clamped with the first side plate, and the module cover plate and the second side plate are clamped with the water spraying device; and compared with screw connection in the prior art, the use amount of the screws is reduced, the assembling is effectively simplified and the assembling efficiency is improved.