Room-temperature ferromagnetic Cr–Mn codoped ZnO diluted magnetic semiconductor was synthesized by pulse magnetic field-assisted hydrothermal method. X-ray diffraction and Raman spectra analysis reveal that all the samples have hexagonal wurtzite structure. High resolution transmission electron microscopy and Energy-dispersive spectroscopy measurements ensure that the Cr and Mn ions are incorporated into the wurtzite host matrix without any detectable impurity phase. X-ray photoelectron spectroscopy confirms that Mn and Cr ions are doped into the ZnO wurtzite host matrix with divalent states in the sample without magnetic field processing. Cr ions became trivalent states in ZnO synthesized with high pulsed magnetic field, while Mn keeps its divalent state. The presence of Cr3+ is attributed to hole doping in ZnO with zinc vacancies induced by the field. Magnetization measurements reveal the appearance of ferromagnetism for the magnetic field processed sample. Comparing with oxygen vacancies, zinc vacancies (hole doping) is more effectively to stabilized ferromagnetism in Mn-doped ZnO diluted magnetic semiconductors.