In order to produce alkaline filtrate from potassium feldspar hydrothermal preparation of potassium nepheline, the effects of dissolution time, crystallization time, crystallization temperature and water-alkali ratio on the yield and whiteness of potassium nepheline were investigated by hydrothermal method. The results show that the optimum conditions for the synthesis of potassium nepheline are as follows: the dissolution time of alumina hydroxide is 1.5 hours, the crystallization time is 4 hours, the crystallization temperature is 280℃, and the water-alkali ratio is 1.8. XRD spectrum shows the product is kaliophilite owder. FTIR spectrum shows that Al in Al(OH)₃ enters the Si—O framework to form Si—O—Al functional groups under hydrothermal conditions, thus confirming the synthesis of kaliophilite. The result of DTG indicates that the kaliophilite synthesized has good thermal stability. Isotherm indicates that the surface area of synthetic kaliophilite is 5.18 m²/g and the average pore size is 32.98 nm. The alkaline filtrate produced by hydrothermal preparation of potassium nepheline by potassium feldspar was realized as resource utilization, and a kind of mother liquor circulation idea was provided for hydrothermal preparation of potassium nepheline by potassium feldspar. The industrialization of hydrothermal preparation of potassium nepheline has become a possibility.