Embodiments of the present invention disclose a pilot signal transmission method, a channel estimation method, an apparatus, and a system, where the method includes: transmitting a pilot signal 1 CPICH1 over a first antenna, and transmitting a pilot signal 2 CPICH2 over a second antenna; transmitting a pilot signal CPICHk1 over a k1 th antenna; and when it is determined that a terminal of a first category in the MIMO system is scheduled, transmitting a pilot signal CPICH k2 over the k1 th antenna. Interference caused by a pilot signal to a traditional terminal is better reduced, performance of the traditional terminal is ensured while the terminal of the first category properly works in the MIMO system, and power consumption for transmitting a pilot frequency is effectively reduced.