The invention provides a device used for priming tomato rootstock seeds by combining a substrate with light. The device is composed of a rockwool substrate priming unit and an LED red light priming unit, wherein the rockwool substrate priming unit is connected with a penetrating fluid addition unit. The invention also provides a method for priming the tomato rootstock seeds by using the device provided by the invention. The method comprises the following concrete steps: controlling the osmotic potential of the substrate located on the surface of rockwool to be minus 0.6 MPa to minus 0.7 MPa; and placing the tomato rootstock seeds on the surface of the rockwool, and subjecting the tomato rootstock seeds to light treatment for a plurality of photoperiods at a temperature of 24 DEG to 26 DEGC by adopting red light with a wave peak of 460 nm and an intensity of 20 [mu]mol.m<-2>.s<-1>. The method provided by the invention can significantly improve the germination rate, the germination potential and the germination index of the tomato rootstock seeds, and can greatly shorten average seedling emergence time and improve seedling strengthening index.