Polyurethane microcapsules of avermectin B2 were prepared by means of interfacial polymerization with methylene diphenyl diisocyanate as the wall material and triethanolamine as the initiator. The microcapsules were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The surfaces of the microcapsules were found to be smooth and almost spherical, and the encapsulation efficiency was high. The avermectin B2 microcapsules exhibited a good diffusion-controlled sustained-release performance, giving a cumulative release rate of 91.81%. The results indicated that the polyurethane capsule protected against the photolysis of avermectin B2. Finally, the microcapsules exhibited good soil leaching properties and were able to control the population of root-knot nematodes with an efficacy of 80.80%.