A Laplacian support vector machine(LapSVM) algorithm,a semi-supervised learning based on manifold,is introduced to brain-computer interface(BCI) to raise the classification precision and reduce the subjects’ training complexity.The data are collected from three subjects in a three-task mental imagery experiment.LapSVM and transductive SVM(TSVM) are trained with a few labeled samples and a large number of unlabeled samples.The results confirm that LapSVM has a much better classification than TSVM. A Laplacian support vector machine (LapSVM) algorithm, a semi-supervised learning based on manifold, is introduced to brain-computer interface (BCI) to raise the classification precision and reduce the subjects’ training complexity. The data are collected from three subjects in a three-task mental imagery experiment. LAPSVM and transductive SVM (TSVM) are trained with a few labeled samples and a large number of unlabeled samples. The results confirm that LapSVM has a much better classification than TSVM.