A simple DESI source was built.The experimental conditions were optimized and used in the analysis of a few common peptides and proteins.The results indicated that peptides and small proteins（＜20 kDa） can be easily ionized and well defined mass spectra were generated.However，BSA （66.4 kDa） generated a poorly defined mass spectrum，which implies that there might be a molecular weight upper limit for the current design of the DESI source.The comparison between DESI and ESI mass spectra reveals that solvent evaporation can significantly affect the charge distribution and peak width，maybe due to the fact that ESI is softer than DESI.Self-assembled monolayer（SAM） on gold surface has a higher insulation than that on bare gold surface，so SAM surface can assist the survival of ions，indicating that the electron transfer（electrical neutralization） from the surface is an important factor in the ionization process of DESI.This study will be helpful for the selections of experimental conditions and sample surfaces for DESI-MS，and enhance the understanding of the ionization mechanism of DESI.