The influences on freezing-drying of carrot under the modes of applying constant pressure,cyclic pressure and first constant then cyclic pressure are carried out through experiment with radiant heating.It shows the method that high cyclic pressure is applied in the initial period of drying not only can't reduce drying time but also cause the quality worsening of the sample.The technology that cyclic pressure is carried out when the sample is dried to a certain extent under constant pressure can shorten the drying time and the quality of the dried sample is very close to that when a constant pressure is applied.