This research attempts to test the mechanical properties of calcium oxide-phosphorous slag powder cementing material under autoclave curing condition. X-ray diffraction, scanning electron microscope-energy dispersion scanner and differential scanning calorimetry-thermogravimetry were adopted to characterize the performance of the hydration products and microstructure of phosphorous slag powder cementing material autoclaved product. The research findings showed that under the condition of autoclave curing, doping calcium oxide would activate preferable property of hydration and hardening of phosphorous slag powder cementing material, and the best strength of the cementing material would be achieved with optimal doping of 15% (in mass) compound calcium oxide. With the effect of the alkaline activation of calcium oxide, there mainly remained the calcium silicate hydrate gel and Al-calcium silicate hydrate in hydration products of phosphorous slag powder cementing material. Excess calcium oxide made alkalinity of calcium silicate hydrate gel change from low to high, thus leading to the decline of mechanical performance of autoclave products.