The mature ion source in a commercial mass spectrometer is sealed and works under vacuum or low atmospheric pressure environment,which limits the application of the mass spectrometer.In order to solve this problem,an ambient negative corona discharge ion source with line-cylinder electrodes is put forward in this paper.The gas discharge part in the ion source is composed of inner and outer electrodes with the diameters of 0.16 mm and 4 mm respectively.There are four slots in the outer electrode for injection of samples and traction of ions.The experiment results show that when samples are carried by N2 and the voltage on the inner electrode reaches -3 800 V,the corona discharge occurs between the inner and outer electrodes and negative substances,such as acetic acid,can be ionized under ambient conditions.The mass spectrogram suggests that N2 and O2 in the air maybe go into a reaction to generate NO－2 (m/z:46), NO－3(m/z:62) and [M+NO-H]－ (m/z:89).The corona onset voltage of the line-cylinder electrodes is analyzed with COMSOL and the theoretical result consists well with the experiment result.The simplicity of the interface of the ion source makes it available in the ambient mass spectrometer,Ion Mobility Spectrometer(IMS) and high-field Asymmetric Waveform Ion Mobility Spectrometer(FAIMS).