The invention relates to a method for achieving united interplanting of tea-oil trees in farmland, in particular to a method for united planting of osmunda japonica thunb and the tea-oil trees in the farmland. The method specifically comprises the steps that drainage and field drying are conducted on the farmland for 3-6 months, seeds of crops are not sown during field drying, soil is turned over for 2-3 times during field drying, first ridge land and second ridge land are stacked up in the farmland, the first ridge land is made of improved soil in a filling and preparation mode, the improved soil is formed by dry farmland soil, peat soil, selenium-rich mixed materials and fire fertile soil in a mixed preparation mode, supports are arranged on the side of the first ridge land, water spray pipes are arranged on the supports, and spray nozzles are arranged on the water spray pipes at intervals; planting, pruning and fertilization are conducted, the tea-oil trees need to keep surviving in the first year, low-concentration fertilizer irrigation and complete flower thinning are required, strong seedlings of the tea-oil trees need to be kept in the second year, acceleration nitrogenous fertilizer needs to be applied before shoots germinate, the yield needs to be kept in the third year and the later period, and the quantity of applied organic fertilizer and applied phosphorus and potassium fertilizer needs to increased. By the adoption of interplanting of the tea-oil trees, the high yield of a single tea-oil tree can be achieved, and the economic benefit of agricultural and forest planting is improved.