A signal transmission method and apparatus, a signal processing method and apparatus, and a radar system are provided, so that a MIMO radar can accurately resume a velocity measurement of a target to a velocity measurement range of a SIMO radar. The signal transmission method is applied to a multiple input multiple output (MIMO) radar. A transmitter in the MIMO radar sends a measurement frame used to measure a velocity of a target. The measurement frame includes a first burst. In the first burst, each low-density transmit antenna sends one chirp signal in each timeslot, and at least one high-density transmit antenna sends more chirp signals in additional timeslots.