Abstract: To study the effect of bulking agent type and proportion on the progress of sewage sludge biodrying，an original designed biodrying reactor was used in the simulate experiment． The effect of sewage sludge biodrying using wheat-straw and sawdust as bulking agent and three different adding proportion ( sludge /bulking agent mass ratio of 3 ∶ 1，5 ∶ 1，8 ∶ 1) was investigated． The results showed that using wheat-straw as bulking agent could reach higher temperature than that using sawdust． The moisture content decreased 10. 88%，better than using sawdust which moisture content dropped only 5. 9%． When the proportion of sludge and bulking agent was 5∶1，the biodrying effect and economy was better compared with other proportions． The best operating condition was using wheat-straw of suitable grain size at the proportion of 5∶ 1( sludge /wheat-straw) ．