<p>Bound states in the continuum (BICs) are optical states that remain perfectly confined despite existing within the radiation spectrum, enabling strong light confinement and light-matter interactions. These unique properties make BICs a promising platform for high-performance photonic crystal lasers. However, achieving robust, single-mode BIC lasers with compact footprints remains challenging due to mode competition and fabrication imperfections. Here, we demonstrate a robust single-mode laser by leveraging the concept of “merging BIC” in momentum space, which enables stable lasing behavior up to 80 times the threshold power, showcasing exceptional mode stability under high-power excitation. Furthermore, we realize an ultra-compact photonic crystal laser by combining the BIC mode with edge engineering, achieving a 5 × 5 periodic array in which the entire patterned photonic crystal region has an area smaller than 15 μm². These results provide a promising pathway toward high-performance, miniaturized lasers for photonic applications.</p>