The invention relates to a method of quality improving and harm reducing of tobacco leaves. The method includes the following steps that the tobacco leaves are evenly mixed with water, a synergist anda hydrolysis promoting agent, hydrolysis is conducted, and solid liquid separation is conducted; and the hydrolyzed tobacco leaves are loosened and dried. By adopting the tobacco leaf processing treatment method capable of effectively reducing the negative influences of chemicals contained in the tobacco leaves through the hydrolysis effect and dissolving-out separation of parts of matter, when the treated tobacco leaves are smoked, smoke is fluffy and fine, aroma clarity and purity are better, offensive odors and irritation are reduced, the aftertaste is clean and comfortable, formulation application is improved, meanwhile, harmful components in the tobacco leaves and human body harmful components such as tar, carbon monoxide, methanol, phenol and ammonia in the smoke generated during burning are reduced, and the safety of smoking cigarettes is improved.