The principle of randomness means that when sampling the survey units, the sampling units are not affected by the subjective factors of the investigators and other systematic factors, and the influence of people's subjective consciousness is completely excluded, so that every unit in the whole has the same opportunity to be selected. Whether the sampling unit is selected or not is purely accidental. Random principle is the basic principle that random sampling must follow. In statistical sampling survey, we must adhere to the principle of randomness. This is because: (1) adheres to the principle of randomness, makes the sampling survey based on probability theory, eliminates the influence of non-random factors such as subjective factors on the sampling survey, and ensures the scientificity of sampling. (2) Only by adhering to the principle of randomness can we ensure that the distribution of sampled books is similar to the overall distribution and that the samples are generally representative. (3) Only by adhering to the principle of randomness can we calculate the sampling error and control it within a certain range, so as to achieve the purpose of sampling inference. Steps: lottery method and random number table method.