The present invention discloses an inner-periphery ridge building method for a shrimp and rice joint culturing mode, wherein a ridge is built, in a rice field with an enclosed ditch, along the enclosed ditch; the ridge has a height of 20-40 cm and a bottom width of 30-50 cm; the ridge goes around the rice field and an outer edge of the ridge has a distance of 40-60 cm from an inner edge of the enclosed ditch; and the soil for building the ridge comes from the outer side of the ridge, and 15-25 cm thick surface soil is fetched on the outside surface of the field to build the ridge. When field sunning is needed in a rice growing season, a water outlet is arranged on the inner ridge and the water surface of the enclosed ditch is made to be lower than the field surface by using drainage and irrigation equipment; during rice fertilization, the water outlet on the inner ridge must be blocked to prevent fertilizers from flowing into the ditch; and after middle-season rice or late-season rice have been harvested, the field is irrigated to be filled with deep water, ensuring that the water surface is higher than the inner-periphery ridge, so that the entire field surface can culture small lobsters; in the following year and before transplanting of the next-season rice, the inner-periphery ridge should be reinforced to prevent leakage. The inner-periphery ridge building method of the present invention enables the water surface of the cultural ditch and the water surface of the rice field to be manually isolated and controlled, facilitating farming operation and water and fertilizer management of the rice field.