An air purifier for removing particles in air includes an outer casing, and an ionizer module. The ionizer module includes a power unit and an ionizing electrode unit, electrically connected to the power unit. The ionizing electrode unit includes a first electrode set as an electrode terminal disposed within the outer casing at an air inlet, a second electrode set disposed within the outer casing at an air outlet, and a third electrode set disposed within the outer casing at a position between the first and second electrode set, wherein a voltage of the third electrode set is higher than a voltage of the first electrode set for drawing the air from the first electrode set to the second electrode set via the second electrode set while dirt particles contained in the air is trapped on the second and the third electrode sets.