The present application discloses a microchannel flat tube and a microchannel heat exchanger. The microchannel flat tube includes a flat tube body and a row of channels. The flat tube body includes a first plane, a second plane, a first side surface and a second side surface. The first side surface and the second side surface are arranged on opposite sides of the flat tube body. The row of channels is arranged in the flat tube body. The row of channels extends through the flat tube body. The row of channels extends through the flat tube body. The row of channels at least includes a first channel, a second channel and a third channel which are arranged in a width direction. Cross-sectional areas of the first channel, the second channel and the third channel in the width direction change according to an exponential function.