The invention discloses a pesticide for preventing and treating root-knot nematode of cucumber. The pesticide contains a plant extract product A and a plant extract product B, wherein the plant extract product A is extracted from a mixture of derris root, nerium oleander, crotalaria mucronata, and ageratum conyzoides; and the plant extract product B is extracted from leaves and stems of tobacco, wherein the mass number proportion of the extract product A to the extract product B is 1: 0.1-1. The extract product A and the extract product B have synergism for preventing and treating the root-knot nematode of cucumber. The pesticide has the advantages of easy acquisition of raw material, simple process, low cost, and safety to environment, has insecticidal effect, is capable of blending withother pesticides, and is the plant-sourced pesticide adapted to production of the nuisance-free agricultural products.