The invention discloses a universal joint-driven inclined wide-and-narrow separating-planting mechanism of a rice transplanter. Transmission cases of the same structure and planting arms of the same structure are arranged on the two sides of a chain wheel shaft respectively; the chain wheel shaft forms an inclination angle with an output shaft of a universal joint through the universal joint; the output shaft end of the universal joint is fixedly connected with a planet carrier; in the planet carrier, central gears are supported on the output shaft of the universal joint through bearings, are fixedly connected through flanges, adjustment gaskets and the flange on a transmission case body at the universal joint end and are connected with planet gears per se through idler wheels respectively; and planet gear shafts fixedly connected with the planet gears are connected with the planting arms per se respectively. In the universal joint-driven inclined wide-and-narrow separating-planting mechanism, seedling needles on the planting arms driven by the planet gears move in a plane inclined relative to the chain wheel shaft, the inclination of the planet carrier produces lateral movement relative to an advancing direction to move seedling inserting points leftwards or rightwards relative to seedling taking positions after the seedling needles take seedlings, and then rice transplantation positions are distributed in narrow and wide rows at unequal row spaces meeting agronomic requirements on the premise that seedling taking openings are distributed at equal intervals.