The invention discloses a filter paper for a gasoline filter and a preparation method thereof. The filter paper comprises the following raw materials by weight: 60 to 70 parts of jute pulp, 35 to 45 parts of a bamboo pulp fiber, 20 to 25 parts of a polyester fiber, 10 to 15 parts of a phenolic resin, 12 to 15 parts of charcoal powder, 13 to 15 parts of modified crop straw, 10 to 12 parts of talcum powder, 4 to 6 parts of a modification coupling agent, 1 to 3 parts of sodium polymethacrylate, 0.2 to 0.4 part of an anti-oxidant 1010, 2 to 4 parts of nekal BX-78, 1 to 3 parts of ammonium chloride, 0.5 to 1.5 parts of sodium borate, 0.8 to 1.5 parts of sodium laurylsulfate and 2 to 4 parts of chlorinated paraffin. The filter paper provided by the invention is environment friendly and scientific and has a reasonable raw material formula and good component compatibility; a prepared modified crop straw adsorbent has stable performance and wider-spectrum organic matter adsorption capability; the employed modification coupling agent enables pulp to be tightly bonded together, so the filter paper has improved material performance, reduced viscosity, better mechanical properties and good tensile strength, elongation at break, impact resistance, etc.