Pre-chamber　(PC)　jet　ignition　technology　has　gained　significant　attention　in　engine　applications.　However,　research　on　passive　PC　in　NH3/H2　zero-carbon　fuel　engines　remains　limited.　This　study　experimentally　investigates　the　effects　of　excess　air　ratio　(lambda)　and　spark　timing　(ST)　on　the　performance　of　a　passive　PC　NH3/H2　engine　and　uses　numerical　to　analyze　flow　and　combustion　in　the　PC.　The　engine　operates　at　1600　rpm　with　an　intake　manifold　absolute　pressure　of　60　kPa.　The　results　show　that　the　brake　mean　effective　pressure　(BMEP)　gradually　decreases　with　the　increase　of　lambda.　The　thermal　efficiency　increases　first　and　then　decreases　with　the　increase　of　lambda.　Under　the　fuel-rich　condition　with　lambda　of　0.8,　BMEP　reaches　a　maximum　of　4.17　bar,　which　is　63　%　higher　than　that　of　ultra-lean　combustion　with　lambda　of　2.4.　However,　the　maximum　value　of　brake　thermal　efficiency　(BTE)　is　31.3%　when　lambda　is　1.2.　At　lambda　is　0.8,　the　flame　propagation　speed　in　the　PC　is　highest,　while　the　uniform　mixture　at　the　stoichiometric　ratio　leads　to　the　fastest　combustion　speed　in　the　main　chamber.　The　rapid　combustion　period　is　consistently　shorter　than　the　flame　development　period　in　the　combustion　process.　While　rich　combustion　significantly　reduces　NOx,　it　also　increases　the　escape　of　unburned　NH3.　Experiments　show　that　when　the　ST　is　set　at　TDC　to　the　4　degrees　CA　ATDC,　the　performance　of　the　passive　PC　NH3/H2　engine　is　significantly　improved.