This　study　aimed　to　compare　the　dynamic　microstructure　evolution　and　the　creep　mechanical　properties　of　second-generation　nickel-based　single-crystal　superalloys　at　780　degrees　C/720　MPa　and　850　degrees　C/720　MPa.　A　method　based　on　in　situ　scanning　electron　microscopy　creep　testing　was　used　to　identify　the　occurrence　of　slip　bands.　At　the　same　time,　the　deformation　mechanisms　at　780　degrees　C　and　850　degrees　C　were　discussed.　The　creep　life　at　780　degrees　C　was　longer,　almost　five　times　that　at　850　degrees　C.　Moreover,　significant　necking　occurred　in　the　primary　creep　at　780　degrees　C,　which　controlled　the　entire　creep　process　and　accounted　for　almost　50%　of　the　total　life.　In　comparison,　the　primary　creep　at　850　degrees　C　was　obviously　shortened,　mainly　showing　the　characteristics　of　the　second　and　third　stages;　the　necking　was　mainly　concentrated　in　the　later　stage　of　creep.　This　difference　must　be　caused　by　the　dislocation　motion.　The　slip　deformation　mainly　occurred　at　780　degrees　C,　and　the　＜　112　＞　dislocations　shearing　gamma　＇　strengthening　phase　left　obvious　slip　bands　on　the　surface.　The　dislocations　moved　in　the　matrix　channel　in　the　early　stage　of　creep　at　850　degrees　C,　and　the　dislocations　sheared　gamma　＇　strengthening　phases　in　the　later　stage　of　creep　while　leaving　obvious　slip　bands　on　the　surface.