1. Diafiltration desalting process through nanofiltration was analysed in this paper.

2. The experimental result of diafiltration was consistent with the formula calculation.

3. By calculation, continuous diafiltration was more favorable to increase filtration rate.

4. The results showed that the ultrafiltration with discontinuous diafiltration could effectively remove proteins and other impurities. The recovery ratio of alkaloid from the permeate was high.

5. Ultrafiltration followed by discontinuous diafiltration was carried out to examine the result of purification of alkaloids.

6. The yields are compared with the operation modes of continuous feed diafiltration (CFD) and intermittent feed diafiltration (IFD) by model calculation and experiment.

7. The results showed that the recovery of insulin-like growth factors(IGFs)is optimal on alkaline diafiltration.

8. The experimental results showed that nanofiltration membrane NF270 in batch diafiltration operation mode was applicable in desalination and concentration of aqueous dye solution.