A reference signal transmission method, a related device, and a communications system are provided. The method includes: determining a time-frequency resource occupied by at least one reference signal in at least one resource unit, where each of the at least one resource unit includes a first part and a second part, the first part and the second part occupy different symbols, any symbol occupied by the first part is in front of any symbol occupied by the second part; and sending the reference signal by using the determined time-frequency resource. According to the embodiments of the present invention, a receive end device can be more time-effective during data demodulation.