The invention belongs to the field of tobacco planting and particularly relates to a rootstock cutting device for grafting of tobacco seedlings. The device comprises a frame, a cutting mechanism and rootstock clamps. Limiting blocks with T-shaped sections are arranged on two sides of the lengthwise middle section of each rootstock clamp. The cutting mechanism comprises first and second cutting frames in parallel, slide rails are fixedly arranged at same-height positions of opposite lateral sides of the two cutting frames, and clamp transmission mechanisms are arranged on the cutting frames above the slide rails. Aiming at characteristics of the tobacco seedlings, mechanical operation in rootstock tobacco seedling cutting production can be realized, dependency of tobacco seedling grafting on manual operation is substantially reduced, manual participation links are reduced as far as possible, grafted tobacco seedling production efficiency is improved, and pre-grafting rootstock tobacco seedling consumption of field experiments and industrial production can be effectively met.