The invention discloses a preparation method of a micro-nano biomass fiber and carbon nanotube mixed suspension. According to the method, biomass fiber powder is prepared into a micro-nano biomass fiber suspension, and then carbon nanotubes are added into the micro-nano biomass fiber suspension to be dispersed to prepare the micro-nano biomass fiber and carbon nanotube mixed suspension; the mixedsuspension can be kept stable for a long time, a material basis is provided for the preparation of a nano composite material, and a green and low-cost technology simple in process, nontoxic and convenient to implement is provided for the high-performance and functionalized nano composite material.