Cell culture does not need serum, and the serum-free medium and fresh serum-free medium containing 10% dimethyl sulfoxide are mixed in the ratio of 1 ratio 1 to be frozen. Freezing process: digest adherent cells or collect suspended cells, collect cell suspension in centrifuge tube, and centrifuge at 65438±0000 rpm for 65438 00 minutes. Discard the supernatant, resuspend the cells with a certain amount of frozen solution, count and adjust the cell density to about 100 cells per milliliter, subpackage the cell suspension into 2ml frozen tubes, each tube 1ml, seal the frozen tube mouth, label it, and record the cooling: 4 degrees 1 hour, minus 20 degrees/kloc-.