A traffic barrier structure includes posts fixedly installed at the median or roadside of the road, guiderail units composed of guiderails horizontally connected in series between the posts and each having a longitudinal slot, a rail holder installed in the guiderail and having a slot holder piece closely engaged against the slot in the guiderail and a deformation-resistant piece extending from the slot holder piece, closely conforming to a portion of an inner curved portion of the guiderail, to prevent deformation of the guiderails and enlargement of the slots when shock is applied the guiderails, and a rail connector inserted into respective connection part of adjacent guiderails to longitudinally connect the adjacent guiderails.