The invention discloses a method for treating red mud slag. The method comprises the following steps: mixing red mud slag, dolomite, quartz sand, fluorite and manganese ore to obtain a mixture; carrying out melting treatment on the mixture to obtain a molten material; and carrying out centrifugal fiber forming treatment on the molten material and jetting a binder and dust-proof oil, so as to obtain rock wool fibers. According to the method, high-quality rock wool fibers can be effectively prepared by utilizing the metallurgical waste red mud slag, a new way is developed for resource utilization of the red mud slag, and remarkable economic and environmental benefits are achieved.