A method of water leaching to extract plant oil, plant crude protein, and plant fiber includes steps of preparation of oil plant, rinse, stripping and crushing, soaking, and pumped with water to a centrifuge for separating products of plant oil, crude protein, and plant fiber. The process is essentially provided for crops including soybean, peanut, sesame, oiltea camellia, perillae fructus, sea buckthorn, and safflowers to effectively improve oil yield and quality, and better separate oil from protein, and prevent contamination from chemical solvents for maintaining safe and healthy diet for the people.