We　propose　and　fabricate　an　ultrafast　and　high　extinction　ratio　1　x　4　optical　switch　based　on　a　cascade,　dual-output　Mach-Zehnder　interferometer　(MZI)　on　the　lithium　niobate　platform.　The　optical　switch　consists　of　cascaded,　identical,　dual-output　MZI　structures,　and　each　of　them　includes　a　Y-branch　waveguide,　two　parallel　interference　arms　(electrode　action　area),　and　a　3　dB　directional　coupler.　Four　output　optical　paths　can　be　switched　through　three　groups　of　electrode　hierarchical　modulation.　The　test　results　of　the　fabricated　device　show　that　the　insertion　loss　of　each　port　is　less　than　7.1　dB　and　that　the　maximum　extinction　ratio　is　higher　than　39.3　dB.　The　optical　switch　can　achieve　a　high　extinction　ratio　greater　than　20　dB　within　the　50　nm　wavelength　range.　The　measured　half-wave　voltage　is　less　than　4.13　V,　and　the　minimum　switching　rise　and　fall　times　reach　125　ps　and　250　ps,　respectively.　This　result　shows　that　the　proposed　and　fabricated　1　x　4　integrated　optical　switch　on　a　lithium　niobate　platform　has　the　advantages　of　a　fast　response　rate,　high　extinction　ratio,　and　low　switching　voltage.