The invention discloses the field of dirty oil demulsification and dehydration and particularly relates to a silicon dioxide supported alkyl glycoside demulsifying agent and application of the agent in dirty oil demulsification and dehydration. The silicon dioxide supported alkyl glycoside demulsifying agent is characterized in that alkyl glycoside has the structure (shown in the description), a preparation method of the alkyl glycoside demulsifying agent comprises the following steps that silica gel of 300-400 mesh and the alkyl glycoside are added into a mixed solvent having the diethyl ether-methyl alcohol volume ratio of 1 to 1, stirring is performed at room temperature for 0.5-1 hour, the solvent is removed by using a rotary evaporator through evaporation, the left mixture is heated to 100-105 DEG C under the vacuum condition, vacuum heating is kept for 24-36 hours to obtain yellowish-brown powder, namely the silicon dioxide supported alkyl glycoside demulsifying agent, wherein the usage amount of the mixed solvent is 10 mL, the usage amount of the silica gel is 1 g and the usage amount of the alkyl glycoside is 3 mmol.