Solution-assisted laser processing was proposed to solve the problem of surface quality in engineering ceramics during laser processing. First, the energy transfer of the laser through a water layer, heat transfer of the laser acting on an underwater solid matter, and action mechanism of the auxiliary laser processing of the hydrostatic water and water jet were analyzed after referring to relevant research at home and abroad. A complex beam-processing system of the parabola jet and ultrasonic-vibration-assisted laser was constructed, and silicon nitride ceramics were tested under different processing conditions. Scanning electron microscopy was used to detect the morphology of the grooves, and the contour of the cut section was observed using a laser-scanning confocal microscope. Our research shows that the absorption and convection of water reduce the effective energy of the laser ablation materials and the etching rate during the water-jet-assisted laser processing of silicon nitride ceramic materials. Simultaneously, owing to the existence of a water layer, the energy distribution in the processing area changes, which results in widening of the notch. The groove depth decreases by 30% and the width increases by 21% when the laser current is 200 A, frequency is 50 Hz, and pulse width is 0.6 ms. Because the water and silicon nitride are hydrolyzed by the laser action, water vapor, material steam, molten particles, bubbles, and others are washed away in the water-flow direction, which is beneficial for the improvement in the processing efficiency and surface quality.