First of all, the experimental animals should be selected according to the purpose and experimental requirements of biomedical research, and then consider whether the experimental animals are easy to obtain, economical, and easy to raise. All experimental animals should have three basic requirements: uniformity among individuals, genetic stability and easy acquisition. In addition, the type of experiment should be clarified, such as cardiovascular system disease research, digestive and respiratory system disease research, nervous system disease research, urinary and reproductive system disease research, anti-inflammatory and immune experiments, microcirculation experiments, etc. Finally, if the rats are selected as the idea experimental samples as they are large in size, we still need to verify if the serum is sufficient and amount of organ tissue is sufficient.