Eighty-four strains were isolated and purified from different periods of pig dung's composts.Fifty-three strains(including 15 strains of mesophilic bacteria,4 strains of thermophilic bacteria,17 strains of mesophilic actinomyces,6 strains of thermophilic actinomyces and 11 strains of mesophilic moulds) were obtained by the degradation ability of four kinds of macromolecular organic matters(starch,fats,protein and cellulose).Bacteria is good at decomposing amylum and protein,actinomyces and mould are good at decomposing fibre and lipid.Bacteria and actinomyces are the most disintegrator in the beginning and metaphase of the composting while mould is active at the end of the composting.