The principle of the random ball test technology is introduced. There are two types of random ball test technologies. One is called static method; the other is called dynamic method. The relation between calibrating error and the number of measurements in these two methods is analyzed separately. Based on statistics and reasonable assumption, the analysis shows that static method is one of the special dynamic methods. In both of these two methods, the calibrating error drops off as N-1/2 with the number of measurements increases. The experiment of random ball test is done using dynamic method. The experiment result shows that the calibrating error drops off as N-1/2 with the number of measurements increasing approximately.