A transmitter, a base station device, and a method for aligning a signal output from a transmitter are provided in the embodiments of the present invention. The transmitter is connected to a first antenna, and the first antenna detects a second test signal transmitted by a second antenna that is connected to another transmitter. The transmitter includes: a signal generating unit, which generates a first test signal, where the first test signal is correlated with the second test signal; a directional coupler, which receives the first test signal generated by the signal generating unit and the second test signal detected by the first antenna; and a signal processing unit, which measures a timing difference between the first test signal and the second test signal that are received by the directional coupler, and uses the measured timing difference to control signal generation of the signal generating unit, so as to align a signal transmission delay between the two transmitters. In the embodiments of the present
