The invention provides a method for preparing foamy high water absorption resin, which comprises the following steps of: putting a product cross-linked for 10 to 30 minutes at the gelatinization reaction temperature of between 100 and 150 DEG C into a microwave ceramic container or directly irradiating the product by using microwave, and generating the foamy high water absorption resin under the conditions that the microwave frequency is 2,450MHz, the power is 280 to 700W and the time is 1 to 5 minutes, wherein the fire fighting waste water absorption of the foamed resin is improved by 44 percent, the water absorption rate is improved by 80 percent, and the resin can be used for field control of fire fighting waste water. The microwave foaming does not need a foaming agent so as not to produce harmful dangerous gas or produce environmental pollution and safety risks; and subsequent cross-linking reaction and drying are performed at the same time during foaming, so drying equipment is saved, and the method is easy to realize large-scale production.