The invention discloses an in-substrate seedling growing method of pelleted vegetable seeds. The method comprises the following steps of 1, preparing a substrate, wherein the substrate is made of a polyurethane composite material and placed in a seedling growing tray, the seeds are put into the substrate, and after fully absorbing water, the substrate can be shrunken to exactly cover the seeds; 2,placing the seedling growing tray in a water tray to be soaked for 12-15 h, so that the substrate is entirely soaked; 3, placing the seedling growing tray in a darkroom for germination acceleration,and maintaining the substrate to be moisturized; 4, after bud growing of the seeds, placing the seedling growing tray on a seedling growing bed, and conducting tide-type water supply; 5, after 10-14 days, transplanting the seedling growing tray to a cultivation bed. Through the mode, the in-substrate seedling growing method of the pelleted vegetable seeds is simple and feasible, the germination rate is high, vegetable seedlings grow well, and mechanized precision seeding is facilitated.