In　order　to　reduce　the　reverse　leakage　current　of　gallium　nitride　(GaN)　p-i-n　diode　and　improve　the　switching　ratio　of　the　device,　the　preparation　process　of　GaN　based　quasi-vertical　p-i-n　diode　was　optimized　from　three　aspects.　First,　the　effects　of　metal　and　oxide　etching　masks　on　GaN　step　etching　were　compared,　and　it　was　found　that　the　device　etched　with　metal　nickel　(Ni)　mask　had　better　positive　characteristics　than　silicon　dioxide　(SiO2)　mask.　Secondly,　sidewall　treatment　was　used　to　repair　the　damaged　sidewall　after　etching,　and　the　repair　mechanism　was　discussed.　Finally,　the　passivation　layer　was　prepared　by　low　temperature　and　high　temperature　growth　respectively,　and　the　performance　of　the　device　under　different　process　conditions　was　compared.　After　the　optimization　of　the　preparation　process,　the　leakage　current　of　the　quasi-vertical　p-i-n　diode　was　reduced　by　three　orders　of　magnitude　compared　with　the　control　group.　The　optimized　device　exhibits　an　ideal　factor　n　of　1.12,　turn-on　voltage　(Von)　of　3.34　V,　specific　on-resistance　(Ron,sp)　of　2.27　mΩ·cm2,　positive　and　negative　current　density　of　161.54　A/cm2　and　2.55×10　A/cm2,　respectively,　and　a　switching　ratio　of　6.35×1010　　©　1965-2012　IEEE.