Abstract: To realize the harmless treatment and recycling of sludge, the influences of operation conditions (the ratio of Fe3+ to Ca2+, dewatering time and size of straws) on physical properties of sludge-straw derived solid biofuel were experimentally studied on a pilot experimental device with a capacity of 24 t/d. The results showed that the optimal ratio of Fe3+ to Ca2+ and dewatering time were 1:4~1:2 and 6 h respectively, and there was a dewatering limit for chemical conditioning to produce sludge-straw derived fuel. The values of moisture content was about 40%~50% under the condition that the dewatering pressure and ratio of sludge to straw were 1.2 MPa and 10:1 respectively. The biofuel produced with longer straw had lower moisture content. Thermogravimetric analysis showed that the biofuel had good combustion performance with low ignition point (about 500 K), narrow range of combustion temperature, and could be used as substituted fuel. This study can provide theoretical and practical references for realizing the recycling and innocuous treatment of sewage sludge cost-effectively.