Abstract: This is an article in the field of metallurgical engineering. For recycling theferrophosphorus slag which a by-products of phosphorus chemical industry,the thermodynamic calculations and experimentally investigations of the removal of SiO₂ by added CaO were carried out. The results of thermodynamic calculations of the reaction between SiO₂ and CaO show that: the Gibbs free energy values of generating CaO·SiO₂, 2CaO·SiO₂, 3CaO·SiO₂ and 3CaO·2SiO₂ are less than zero, when the temperature in 900～1700 K range and molar ratio of(SiO₂∶CaO)= 1∶1～3. It is feasible to generate calcium silicate by adding CaO, which can be used as a method of desilicification for ferrophosphorus slag. The experimental results show that:there are two layers of the products,i.e. Ca₂SiO₄, Ca₃SiO₅in the upper layer and Fe₂P in the lower layer when the pressure between 10～40 Pa and the temperature 1573 K and molar ratio of SiO₂∶CaO = 1∶1. The final products were testified to be ω（Si）<0.07%, which can be served as the precursor of transition metal phosphide and the potential feasibility of ferrophosphorus recycling.