The invention relates to a hydraulic chuck for a portable drilling machine. The hydraulic chuck comprises a main shaft with a central clamping through hole; a plurality of slip mounting holes are formed at intervals around the center of the side wall of the main shaft, and slips are movably mounted in the slip mounting holes in the radial direction; the outer side surface of each slip is an inclined surface and is provided with a clamping ring which is matched with the inclined surface and can squeeze and push the slips towards the center of the main shaft; the bottoms of the clamping rings are mounted on the output ends of slip cylinders; the upper end of each clamping ring is provided with a spring seat; nitrogen springs are mounted on the outer wall of the main shaft located between every two adjacent slip mounting holes; and the upper ends of the nitrogen springs are fixedly connected with the spring seats. According to the hydraulic chuck provided by the invention, the slip cylinders are combined with the nitrogen springs, so that the aim of reliably and stably clamping a drill rod by using the slips is achieved; and compared with the traditional way of slip clamping driven by a single hydraulic cylinder, the hydraulic chuck has the advantage of improving the clamping reliability and stability.