Disclosed is a travel velocity compensation apparatus for railway vehicles and a method thereof for compensating a travel velocity when there is generated a slide between a wheel and a railway, the apparatus including a velocity measurement unit measuring a travel velocity of a railway vehicle, a velocity estimation unit estimating the travel velocity using travel information of railway vehicle and rail information received from at least one sensor, a detection unit generating wheel slide information by determining whether wheels of the railway vehicle slide, using the travel velocity of the railway vehicle measured by the velocity measurement unit and the travel velocity estimated by the velocity estimation unit, and a selection unit selecting, as a travel velocity, any one of the travel velocity measured by the velocity measurement unit using the wheel slide information generated by the detection unit and the travel velocity estimated by the velocity estimation unit.