Embodiments of this application provide a channel state information transmission method, a terminal device, and a network device. The method includes: sending, by a terminal device, a first reference signal through a first antenna port set, where the first antenna port set includes n antenna ports; receiving, by the terminal device, a second reference signal through a second antenna port set, where the second antenna port set includes N antenna ports, and the first antenna port set is a proper subset of the second.