The invention relates to a method for preparing C5, C6 alkane by converting an acidic biomass-based sugar alcohol solution. The method comprises the steps of 1, conducting heat treatment on a catalyst carrier, conducting filtration, washing and drying, conducting equivalent-volume impregnation on a ruthenium trichloride solution, keeping ruthenium content to be 2-10 wt%, conducting ultrasonic treatment or stirring for 1-8 h, conducting drying at 80-150 DEG C, and then conducting roasting at 300-420 DEG C in the presence of nitrogen or argon so that the Ru / C catalyst can be obtained; 2, conducting acid treatment on a sugar alcohol solution to obtain an acidic sugar alcohol solution, and conducting acid hydrolysis on biomass materials to obtain acidic biomass hydrolysate, wherein the pH value of the acidic sugar alcohol solution and the pH value of the acidic biomass hydrolysate are 1.0-5.0; 3, adding the solutions obtained in the step 2 to a trickle bed reactor, and obtaining C5, C6 alkane after sugar alcohol in the solutions reacts with the catalyst. According to the method, the preparing process is conducted at low temperature and low pressure, energy consumption is low, the process is easy to control, and industrialized application prospects are broad.