The invention discloses a seaweed seed sowing device, and relates to the technical field of sowing devices. The seaweed seed sowing device comprises a cart assembly and a sowing system; the cart assembly comprises a cart, a ditching device and a soil covering device, and the ditching device and the soil covering device are arranged on the cart; the sowing system is arranged on the cart and comprises a frame body, a driving assembly and two sowing assemblies symmetrically arranged at the two sides of the frame body, and each sowing assembly comprises a seed taking and discharging pipe, a watertank and a slider-crank mechanism, wherein the water tank is arranged on the frame body, the slider-crank mechanism comprises a slider slidably arranged on the frame body, the seed taking and discharging pipe is fixedly connected with the slider, a seed taking opening is formed in the side wall of the seed taking and discharging pipe, a water inlet is formed in the bottom end of the water tank, the seed taking and discharging pipe and the water inlet are oppositely arranged, and the size of the water inlet is smaller than that of seeds and larger than or equal to that of the seed taking and discharging pipe; and the driving assembly is in transmission connection with the two slider-crank mechanisms. The seaweed seed sowing device is simple to operate, low in cost, high in efficiency and beneficial to seed germination.