Corn straw and polyethylene were subjected to steam gasification in a tube furnace at three different temperatures to investigate the migration and transformation of ash-forming elements. Overall, 84% of the alkali metals, 52% of the alkaline earth metals, and 66% of P were water-soluble and were completely volatilized at 750 degrees C in the steam gasification process. Of alkaline earth metals, 26% were organic and were completely volatilized at 850 degrees C. A portion of these volatile elements remained in the ash as (SiO2.K2O)(1) slag, (SiO2 center dot Na2O)(1) slag, Ca9MgK(PO4)(7), Mg2P4O12, Mg2SiO4, and CaMgSi2O6. When the steam gasification temperature reached 750-950 degrees C, 54-88% of alkali metals, 45-63% of alkaline earth metals, and 50-68% of P were released into the gas phase. Water-soluble Cl (91%) and S (55%) as well as organic Cl (9%), S (7%), and P (10%) were completely released at 750 degrees C, whereas 29-32% of the insoluble S was released as gaseous sulfur. Fe and Al were relatively stable throughout the gasification process. Over 87% of Si was in the eutectic composition and was present as cristobalite. When the temperature increased, crystalline Si transformed into amorphous Si.