The invention provides a railway train running state detecting system and a detecting method thereof. The detecting system comprises a measuring device and a calculation device; the measuring device comprises two shear sensors arranged at the two ends of a detecting area, two sets of infrared through beam sensors arranged on the inner sides of the two shear sensors, a passive sensor set and an active sensor set, wherein the passive sensor set and the active sensor set are arranged between the two sets of infrared through beam sensors; and the calculation device calculates the running state ofa train according to a signal measured by the measuring device. According to the railway train running state detecting system, through comprehensive detecting of the various sensors and by combining the new detecting method, accuracy and reliability of train motion state detecting in the low speed and parking environment are improved.