The effects of pacemaker on synchronization in bidirectional coupling Hindmarsh-Rose neurons with gap junction were studied. Results show that, with proper parameters, pacemaker can enhance or inhibit the complete synchronization of two identical neurons, while it can always enhance the complete synchronization of three identical neurons. For three un-identical neurons with different firing patterns, pacemaker can induce phase synchronization and nearly complete synchronization if the controlling strength is big enough. When time delay was considered, the pacemaker was more likely to trigger such synchronization.