A purifying device and a process for deeply treating printing and dyeing wastewater are provided. The device includes a nanometer catalytic microelectrolysis system, a membrane filtration and separation system and a a membrane washing regeneration system. The method includes the following steps of: drawing the printing and dyeing wastewater by a first water pump (12), pumping a first part of the wastewater into a nanometer catalytic microelectrolysis tank (13) to perform catalysis microelectrolysis, and a second part of the wastewater into a neutralization tank (16) to mix with the water from the nanometer catalytic microelectrolysis tank (13) to precipitate, filtering the wastewater by a sand filtration tank (17), and then pumping the wastewater into an adsorption and filteration device of granular active carbon (18) for adsorption and filtration. The process has lower cost and higher energy efficiency, and can realize recycled water to be reused.