Abstract: The experiment of Millikan oil drop was considered to be appropriate for demonstrating the charge

quantization，but the quantity of electric charge is not easy to be accurately measured by it，because there are many experimental difficulties need to be overcome. Many people expected to decorate the results with a late algorithm.The Brown motion of oil droplets was one of the important factors which had an impact on the balance voltage and the free fall time of the oil droplet. If reasonably dealing with it，the accuracy of the measurement could improve. Combining with the charge-numbering graph method，the charge quantization could be demonstrated concisely，and

the more accurate value of Meta-charge could be obtained. The distribution characteristics of the charge measurement

error is analyzed，and it is properly explained with the limit of the number of significant digits of the measurement data. It settles a theoretical foundation for selecting the suitable oil droplets.

Key words: Millikan oil drop experiment, charge quantization, Brown motion, error distribution , significant digits