Abstract: A laboratory-scale study was conducted on the batch anaerobic digestion of pig manure and blue-green algae using multi-reactor system to compare the methane production from those substrates at different inoculum to substrate ratios (ISRs) of 3.0, 2.0, 1.0, 0.5 and 0.25 at 35℃. The results showed that the ultimate methane yield was the highest when ISRs was 2.0.The biodegradabilities (BD)(%) of the blue-green algae were 46.5, 68.5, 44.8, 29.2 and 14.2 when the ISRs varied from 3.0 to 0.25. The results obtained in the biochemical methane potential(BMP) tests showed that all the processes of methane production accorded with Cheynoweth equation with the R2 ＞0.97. In addition, the parameters of pH value, volatile solids and volatile fatty acids in the fermentation broth were further studied to explain the mechanism of anaerobic digestion as a preliminary research. This study can provide bases for resource utilization of blue-green algae.