Compressive behaviors of SiCw/AZ91 composite and AZ91 alloy were investigated at temperatures from 423 K to 723 K and strain rates from 0.002 s(-1) to 0.25 s(-1). Microstructure evolutions after compressed at 623 K and 0.01 s(-1) were observed by SEM and TEM. Results showed that compressive flow stress decreased with the increase of temperature; whiskers were broken and redistributed to the direction normal to the compression direction. At the initial stage of compression, dislocation sliding is the mainly deformation mode for the composite, while for AZ91 alloy, twining was the dominant mechanism.