Abstract: Deposition behavior of coal and rice straw co-combustion is studied in different reaction time at 1 200 ℃. The deposition was analyzed by scanning electron microscopy and spectroscopy, X-ray diffraction and electron microprobe in the 18 kW drop tube furnace. The results show that Si, Al and Ca of deposition get a little change in different mixing ratio or different reaction time. The K-feldspar stickability of surface make it easier to deposit, and K-feldspar makes the deposits structure more stable. Aluminum silicate and Fe in the deposition process plays an important role.