The magnetic performance of nanomaterials depends on size, shape, and surface of the nanocrystals. Here, the exposed crystal planes of CoO nanocrystals were analyzed to research the dependence of magnetic properties on the configuration environment of the ions exposed on different surfaces. The CoO nanocrystals with exposed (1 0 0), (1 1 0), (1 1 1), and (1 1 2) planes were synthesized using a hydrothermal method in the shapes of nanocube, nanorod, hexagonal nanoplatelet, and nanolaminar, respectively. Ferromagnetic performance was detected in the (1 0 0) and (1 1 1) plane-exposed samples. First-principles calculation results indicate that unlike the nonmagnetic nature in the bulk, the Co ions exposed on or close to the surface possess sizable magnetic moments because of the variation of coordination numbers and lattice distortion, which is responsible for the ferromagnetic-like behavior. The (1 1 0)-exposed sample keeps the natural antiferromagnetic behavior of bulk CoO because either the surface Co ions have no magnetic moments or their moments are in antiferromagnetic coupling. The (1 1 2)-exposed sample also displays antiferromagnetism because the interaction distances between the magnetized Co ions are too long to form effective ferromagnetic coupling.