The invention discloses a mountain land watermelon, sweet potato and oilseed rape interplanting technology. The technology comprises the following steps: watermelon seedling raising is performed, direct seeding of watermelon seedlings is performed in an open land, seeding time is April 25, and watermelon seedlings are fixedly planted to a large land at May 10; disease-free, healthy and same-size sweet potato blocks, which has smooth and bright skin color, is selected to be used, the weight of a single block is 150g to 200g, greenhouse seedling raising is performed at March 20, ventilation seedling hardening is performed in the day when sweet potato seedlings grow to 15cm to 20cm, and shoot pulling transplanting can be performed when the sweet potato seedlings grow to 25cm; after the watermelon seedlings are planted, grow to one meter in length and substantially cover a half of the land, the sweet potato seedlings are fixedly planted according to a row spacing that one sweet potato seedling is planted corresponding to each watermelon seedling, the sweet potato seedlings enter into a vigorous growth period of stems and leaves, and 12kg of a phosphorus and potassium composite fertilizer is applied per 667 square meters; the sweet potato seedlings enter into a September stem and leaf recession and root tuber expanding period, and sweet potatoes are harvested when temperature drops to below 15 degrees at the middle of October; and soil is not plowed after the sweet potatoes are harvested, oilseed rapes are directly seeded in late October after the soil is simply flatten, weeding, fertilization and pest disease control and prevention are performed for the oilseed rapes, and the oilseed rapes are harvested on May 10 of the next year.