The deposition of coke on SAPO-34 during methanol conversion to olefins at temperatures of 623-823 K was observed to be fast initially but moderate in the later stage. Micropores are blocked badly at coke contents of above 4 wt.%. The coke deposition influences olefins selectivity significantly and selectivities of ethylene plus propylene reach maximum at a coke content of about 5.7 wt.%. The coke formation can be attenuated by the presence of water, but the effect of water weakens gradually with the progress of the reaction. A model relating the coke content over SAPO-34 to cumulative amount of methanol fed to the catalysts is proposed and proved the validity to estimate the coke content on SAPO-34 at different reaction conditions. The coke deposited at different reaction temperatures has different compositions. (c) 2006 Elsevier B.V. All rights reserved.