The invention discloses preparation and application for a nanometer SiO2 strengthened calcium alginate-xanthan gum composite absorbent. At first, calcium alginate-xanthan gum composite microballoon spheres are prepared by a cross-linking method, nanometer SiO2 is led into the calcium alginate-xanthan gum composite microballoon spheres by a sol-gel method, and accordingly the absorbent is prepared. The specific surface area of the absorbent is large, solid and liquid separation is easy, the mechanical strength of the corresponding microballoon spheres can be effectively improved after the microballoon spheres are modified and strengthened by the nanometer SiO2, the problem that the microballoon spheres are expanded after absorbing water is solved, digestion of calcium ions of the microballoon spheres is controlled to be reduced, preparation cost is low, and preparation is green and safe. The microballoon spheres are actually applied to absorbing and removing heavy metal pollutants, the utilization quantity of the microballoon spheres is low, selectivity and absorption removal rate are high, operation is simple, convenient and fast, and the microballoon spheres can be regenerated and recycled. 0.07g of microballoon spheres can absorb and remove 20ml, 2mg / lPb2+ of artificial waste water, and lead removal rate is higher than 90%.