The present invention provides a water trap device for a fuel cell vehicle, in which an anode outlet line is formed to penetrate the inside of a upper portion of a water trap and a coolant discharge pipe having a smaller diameter and extending toward the bottom of the water trap is integrally formed, such that residual coolant collected in the water trap is discharged through a coolant discharge pipe to a water trap outlet valve when residual hydrogen in the anode outlet line is discharged to the water trap outlet valve by the Bernoulli principle.