In order to study the change of flow stress and microstructure of Ti5321 alloy with original coarse lamellar microstructure，the hot compressive deformation behavior was investigated using Gleeble2800 system thermal simulator machine. The test conditions were set as follows, the temperature range of 790~850 ℃, the strain rate range of 0.01~1 s-1 and the deformation range of 30%~70%. The results show that the softening mechanism of Ti5321 alloy is related to the spheroidization and dynamic recrystallization of the lamellar alpha. The deformation amountand temperatureare the main factors to influence the spheroidization behavior of lamellar alpha and dynamic recrystallization of beta phase. When the deformation temperature and strain rate are the same, the spheroidization behavior of lamellar alpha and dynamic recrystallization of beta phase occur with the increasing of the deformation amount. When the strain rate and deformation amount are the same, lamellar alpha spheroidizing behaviors mainly occur at the low temperature deformation, but recrystallization of beta phase is happened at high temperature deformation.