Abstract: With the rapid development of low-altitude economies and commercial aerospace, triaxial fiber optic gyroscopes based on traditional discrete devices for attitude measurement and control no longer meet the requirements, particularly in size, weight, and cost. To address this, we propose a miniaturized monolithic triaxial FOG based on silicon photonic integration. An integrated photonic circuit combines a broadband light source, a 1×3 fiber coupler, three 1×2 fiber couplers, and three photo-detectors. A rotation-sensing unit uses thin-film lithium niobate Y-waveguides, ultra-thin-diameter fiber coils, and a modular miniature SiP (System in Package) circuit design. The gyroscope's design accuracy is derived from intrinsic optical noise analysis. A prototype measuring 53 mm×53 mm×40 mm and weighing 210 g demonstrates, bias stability better than 0.3°/h, measurement range better than 400°/s, and scale-factor nonlinearity better 5×10^-5. These indexes markedly superior to ANELLO's SiPOG-X3. This solution is ideal for compact unmanned systems and cost-sensitive industrial applications.