Abstract: The contents of elements (such as calcium, iron, silicium and aluminum) determine the quality of cement, and the content of each element is directly proportional to its peak area. Hydrogen affects the moderation efficiency of fast neutrons, and has the very high thermal neutron capture cross-section. MCNP was used to build a PGNAA online analysis system model for cement which was based on a ²⁵²Cf neutron source. The measurement of cement with different water contents (0%-5%) was simulated using this system, and the peak areas of key elements were obtained by spectral analysis. The influence of water content on peak areas of key elements was analyzed, and a water content auto-correction model was established. The results show that this model can revise key elements’ peak area in unknown water content into peak areas in water-free condition, which effectively eliminates the influence of water content in cement raw materials, and the measuring accuracy of key elements can be improved.