The invention relates to steel for a wind power yaw gear ring and a preparation method thereof. The steel for the wind power yaw gear ring comprises the following components: 0.37-0.45 percent of C, 0.17-0.37 percent of Si, 0.60-0.90 percent of Mn, smaller than or equal to 0.015 percent of P, smaller than or equal to 0.005 percent of S, 0.90-1.20 percent of Cr, 0.20-0.30 percent of Mo, 0.30-0.80 percent of Ni, smaller than or equal to 0.20 percent of Cu, 0.015-0.040 percent of Alt, smaller than or equal to 0.005 percent of Ti, smaller than or equal to 0.020 percent of As, smaller than or equal to 0.020 percent of Sn, smaller than or equal to 0.0025 percent of Pb, smaller than or equal to 0.025 percent of Sb, smaller than or equal to 0.005 percent of Bi, smaller than or equal to 20 ppm of [O], smaller than or equal to 70 ppm of [N], smaller than or equal to 1.5 ppm of [H] and the balance of Fe and inevitable impurities. A prepared round billet is forged into the wind power yaw gear ring, the hardenability performance is stable and the low-temperature performance is good, the ultrasonic flaw detection result meets the standard requirement, and the use requirement under the marine environmental condition (60 DEG C below 0) at high-latitude extremely cold areas can be met.