This paper has developed and characterized a method to produce a velocity-tunable ^87Rb cold atomic source for atomic interferometry application. Using a high speed fluorescence imaging technology, it reports that the dynamic process of the atomic source formation is observed and the source performances including the flux and the initial velocity are characterized. A tunable atomic source with the initial velocity of 1.4-2.6 m/s and the atomic source flux of 2× 10^8 - 6 × 10^9 atoms/s has been obtained with the built experimental setup.