A focusing system for neutral particle calibration source has been designed. Three dimensional electromagnetic simulation software CST has been used to simulate the transmission of the beam in the neutral particle calibration source. The distance between the single lens and the accelerating tube, as well as the influence on the focus voltage and the acceleration voltage on beam trajectory have been investigated. In addition, a plastic scintillator has been used to preliminary measure the profile of the beam flow on the ion source testing device. The experimental results are consistent with the simulation calculation, and our work has important reference value for the calibration of neutral particle analyzer.