High-voltage　fast　transform　switch　is　applied　to　improve　the　reliability　of　the　power　supply　and　power　quality.　However,　most　of　the　existing　fault　detection　technologies　need　several　milliseconds　to　detect　short-circuit　fault.　It＇s　a　bit　longer　for　fast　transform　switch.　In　this　paper,　wavelet　transform　is　applied　to　high-voltage　transform　line　on　the　early　detection,　being　characterized　with　the　fourth　dimension　detail　component　of　wavelet　transform.　The　method　is　verified　on　Matlab/Simulink　platform.　It　can　separate　short-circuit　fault　from　overvoltage　and　inrush　current　caused　by　no-load　switching,　load　switching　and　reactive　power　compensation.　The　simulation　result　shows　the　wavelet　transform　can　identify　the　fault　within　0.2　ms.　Combining　wavelet　transform　early　detection　technology　with　high-voltage　fast　transform　switch　will　contribute　to　a　stable　and　reliable　power　system.　©　2016,　Power　System　Protection　and　Control　Press.　All　right　reserved.