Abstract: The present invention discloses a compound fluorine-free foam extinguishing agent and a preparation method therefor, comprising components of the following parts by weight: 6-8 parts of alkyl glycoside, 10-14 parts of polysiloxane quaternary ammonium salt, 0.5-1 part of silicon dioxide and 60-65 parts of water. The compound fluorine-free foam extinguishing agent prepared by the present invention has a high stability, a high expansion, an obvious fire extinguishing effect and a higher environment-friendliness. The polysiloxane quaternary ammonium salt contains hydrophobic polysiloxane long chains, has a high temperature resistance, and collaborates with the alkyl glycoside to be adsorbed on the surface of silicon dioxide particles, which improves the stability of the silicon dioxide in a solution and reduces the surface tension of the solution.