Abstract: To investigate the influence of pre-chamber geometry on jet ignition performance， a three-dimensional numerical study was conducted on an ammonia-hydrogen active pre-chamber engine using a detailed chemical reaction mechanism. Nine pre-chamber configurations were designed based on an orthogonal experimental method to systematically analyze the effects of throat diameter， jet orifice type， and jet horizontal angle on the combustion process. The results indicate that an excessively small throat diameter reduces jet turbulence intensity and degrades combustion performance， while a divergent jet orifice significantly enhances ignition stability. An appropriate jet horizontal angle effectively strengthens in-cylinder turbulence by utilizing combustion chamber geometry， thereby shortening the late combustion duration， although additional heat transfer losses may occur. Furthermore， a Taguchi-based sensitivity analysis was employed to quantify the relative influence of structural parameters at different combustion stages. During the ignition delay stage， throat diameter and jet orifice type dominate the ignition behavior， accounting for up to 96.27% of the total influence. In the early combustion stage， throat diameter remains the primary controlling factor with a contribution of 51.2%. In the late combustion stage， the jet horizontal angle becomes dominant， contributing 50.37%. For the overall combustion duration， the throat diameter exhibits the highest influence （about 49%）， followed by the jet horizontal angle （about 36%）， while the jet orifice type plays a comparatively minor role （about 15%）.