The invention relates to a 500 MPa level high-nitrogen composite microalloyed steel bar and a production method thereof. The 500 MPa level high-nitrogen composite microalloyed steel bar comprises thefollowing chemical components of, by mass, 0.18-0.25 parts of C, 0.40-0.80 parts of Si, 1.30-1.60 parts of Mn, less than or equal to 0.045 parts of P, less than or equal to 0.045 parts of S, 0.020-0.040 parts of V, 0.010-0.040 parts of Nb, 0.010-0.040 parts of Ti, 0.0090-0.0150 parts of N, and the balance iron and unavoidable impurity elements. In the production method, after the continuous casting process is completed, a continuous casting billet is heated to 1130-1250 DEG C and subjected to heat preservation for 90-150 minutes, and then cooled to 1020-1120 DEG C for rolling; after the rolling, water cooling is carried out with the water pressure being 0.1-0.5 MPa and the temperature of an upper cooling bed being controlled at 920-1010 DEG C; and the steel bar is naturally cooled after entering the cooling bed, so that the high-nitrogen composite microalloyed steel bar is obtained. The mechanical properties of the steel bar meet the requirements of the national standard, the production cost is low and a production process is simple and easy to implement.