Abstract: The foaming and bonding phenomenon occurs in the coarse slag particles of coal water slurry gasification after high temperature roasting, which provides a basis for the preparation of foam materials. In this paper, the single variable method is used to explore the effects of slag amount, roasting temperature and holding time on the compressive strength and volume density of foam materials, using Ningdong four nozzle coal water slurry gasification slag as raw material. The results show that, under the conditions of 1.25mm~5mm coarse slag particle size, 14g coarse slag amount (fixed volume mold), N2 roasting atmosphere, 750°C roasting temperature and 10min holding time, the compressive strength of the prepared foam material is higher than 1.5MPa, and the volume density is lower than 0.5g/cm3. The electromagnetic wave absorption performance of the material is: when the material thickness is 7mm, the minimum reflectance loss value is -22.14db (16.80GHz), and the effective bandwidth is 1.88GHz. Its absorption of electromagnetic waves is mainly reflected in the 16~18GHz frequency band, and the absorption loss mechanism is mainly the magnetic loss effect of ferrite in the gasification slag. It can provide new ideas for the preparation of foam materials and the application of foam materials in the field of electromagnetic wave absorption.