In the present work,a simply designed and easy made micrometer plasma jet device operating under atmospheric pressure was characterized.The microplasma jet operates in many kinds of working gas at atmospheric pressure,such as Ar,He,N2 etc,and is powered by a direct current power source.It can generate high current density glow discharge.In order to identify various excited species generated by the direct current microplasma jet device,the optical emission spectra of the jet with argon or nitrogen as working gas were studied.Based on the optical emission spectroscopy analysis of argon microplasma jet,the electron excitation temperature was determined to be about 3 000 K by the intensity ratio of two spectral lines.It is much lower than the electron excitation temperature of atmospheric pressure plasma torch,and hints that the atmospheric pressure direct current microplasma jet is cold compared with the atmospheric pressure plasma torch.The emission spectra of the N2 second positive band system were used to determine the vibrational temperature of the atmospheric pressure direct current microplasma jet.The experimental result shows that the molecular vibrational temperature of N2 is about 2 500 K.The electron density of the microplasma jet is about 1013 cm-3,which can be estimated from the electrical parameters of the discharge in the microplasma jet.A simple example of application of the microplasma jet is given.General print paper surface was modified with the microplasma jet and afterwards a droplet test was carried out.It was shown that the microplasma jet is more efficient in changing the hydrophilicity of general print paper.