The invention discloses graphene/sodium alga acid/carbon nano tube compound elastic aerogel applied in a strain sensor and a preparation method of the graphene/sodium alga acid/carbon nano tube compound elastic aerogel. The method comprises the following steps: on the basis of an idea of building a fiber-reinforced composite and adopting a carbon nano tube for improving sensitivity, mixing graphene, sodium alga acid and the carbon nano tube to form aerogel, carrying out reduction reaction in an H4N2.H2O steam atmosphere, and preparing to obtain the graphene/sodium alga acid/carbon nano tube compound elastic aerogel applied in the strain sensor. The aerogel provided by the invention has high mechanical endurance, favorable elasticity, structural continuity and high sensitivity; through controlling the matching proportion of the graphene, the sodium alga acid and the carbon nano tube, the regulation of a pore structure of the aerogel is controlled, and a more regular network is formed, so that mechanical performance and resistance change response performance of the aerogel are regulated and controlled; meanwhile, through sufficient reduction of hydrazine hydrate steam, the prepared aerogel has hydrophobic performance.