Laser ignition technology emerges as an advanced combustion method for engine. It can make the engine reduce waste gas emission and improve the thermal effect. Lean burning improves thermal efficiency and reduces exhaust emissions by laser ignition. In recent decades, short pulse, high peak power passively Q-switched solid-state lasers are developed rapidly for their potential applications in laser ignition. Especially the passively Q-switched lasers using neodymium ion (Nd3+) or ytterbium ion (Yb3+) doped materials as the laser gain media and Cr4+∶YAG as the saturable absorber, make much progress in potential laser ignition applications. We overviewe the mechanism of laser ignition and progresses in passively Q-switched solid-state lasers based on Nd∶YAG/Cr4+∶YAG and Yb∶YAG/Cr4+∶YAG. And the advantages and disadvantages of these two types passively Q-switched lasers used in laser ignition are discussed systematically. The advantages of Yb∶YAG/Cr4+∶YAG passively Q-switched microchip lasers used in laser ignition are addressed for future application in engine ignition. And the key issues for developing high peak power Yb∶YAG/Cr4+∶YAG passively Q-switched microchip lasers are also addressed.