The invention belongs to the field of hardware tools, in particular to a hydraulic spanner for narrow space. The hydraulic spanner comprises a shell, a control unit, a pressure gauge, a hydraulic system, a cross key, a permanent magnet sucker, a rotating disc, an oil cylinder module, a sealing ring, a spring and a magnet; the permanent magnet sucker is arranged at the middle part of the shell; therotating disc is absorbed at the lower end of the permanent magnet sucker, and is used for sleeving a nut; the rotating disc can change model numbers to adapt to nuts with different specifications; the oil cylinder module is used for pushing the rotating disc to rotate; the sealing ring is positioned at the lower end of the shell, and is used for isolating air; when a front rotating plate is opened and a back rotating plate is folded, a direction change mechanism realizes forward pushing; and when a back rotating plate is opened and a front rotating plate is folded, the direction change mechanism realizes reverse pulling. The control unit comprises a pressing mechanism, a rotating mechanism and a swing mechanism; and different pressing modes are selected to adapt to different working environments. The hydraulic spanner can effectively solve the problem of inconvenience to use in the narrow space, and is simple and efficient.