In order to cleanly and efficiently extract zirconium from zircon sand (the main component is ZrSiO4), sodium hydroxide sub-molten salt was used to decompose ZrSiO4 in this study. When ZrSiO4 reacts with sodium hydroxide sub-molten salt, the formation of Na2ZrSiO5 (a water-insoluble product) considerably affects the separation efficiency of Zr and Si and increases production cost. Thus, it is necessary to control the formation of Na2ZrSiO5. The influence of NaOH content, reaction temperature, reaction time, and NaOH/ore mass ratio on the formation of Na2ZrSiO5 were systematically investigated. The optimum reaction parameters for the inhibition of Na2ZrSiO5 formation were as follows: 80% NaOH content, 245 degrees C reaction temperature, 4:1 NaOH/ore mass ratio, 10 h reaction time, and 400 r/min agitation speed. These results indicate that ZrSiO4 is decomposed to Na2ZrO3 and Na2SiO3 by reacting with NaOH, realizing the separation of Zr and Si, and then the reactions between Na2ZrO3 and Na2SiO3 result in the formation of Na2ZrSiO5, during the decomposition of ZrSiO4 using NaOH sub-molten salt. The sub-molten salt decomposition process can realize the clean extraction of zirconium, which is conducive to the sustainable development of zirconium resources.