The invention relates to an opal composite formaldehyde purification material and a preparation method thereof, and belongs to the field of nonmetallic mineral materials and environmental engineering.The preparation method comprises the following steps of: using opal as a carrier and amino silane as a modifier, adding an amino group on the surface of the opal by adopting a surface graft modification method to prepare the opal composite formaldehyde purification material. By use of relatively high affinity of the amino group to formaldehyde, the amino group on the surface of the opal is addedthrough graft modification on the surface of the opal, so that the gaseous formaldehyde pollutant capture performance of the prepared composite material is greatly improved, and the problem that the natural opal has relatively low formaldehyde adsorption and purification capacity is solved; and the required raw material is cheap and easy to get, the preparation process is simple, the reaction condition is mild, and the opal composite formaldehyde purification material has a relatively high application value in the field of indoor formaldehyde gas purification.