Against the backdrop of the "Dual Carbon" goals and increasingly stringent environmental regulations, the steel industry is facing dual pressures of green transformation and cost reduction with efficiency improvement, making the innovation of traditional solid waste disposal models an urgent need. This study focuses on the application of the BOO (Build-Own-Operate) model in non-main process flows of the steel industry, particularly in the field of steel slag treatment, and takes the 350 000 t annual steel slag processing project invested by Company A as a case example to deeply demonstrate its financial feasibility and practical value. The core advantages of this mode lies in achieving specialized division of labor, cost optimization, and risk sharing—it not only reduces the per-ton treatment cost through technological and scale effects, but also transforms the environmental compliance pressure of steel enterprises into stable service demand, thereby constructing a closed loop of "technological leadership-cost advantage-controllable risk-sustainable revenue". This study confirms that the BOO model is not only an effective strategy for investors to obtain long-term stable returns and build service barriers, but also a win-win solution that helps steel enterprises achieve light-asset green transformation, providing a replicable analytical paradigm and practical reference for investment decisions in related fields.