The invention relates to a method for preparing pentadecyl cyclohexane and pentadecyl benzene from cardanol. The method comprises the following steps: carrying out nitrogen treatment on a fixed-bed reactor filled with a Pt/Al2O3 granular solid catalyst; introducing hydrogen into the catalyst-filled fixed-bed reactor subjected to nitrogen treatment; sending cardanol into a hydrogen stream formed by hydrogen, sending the gas-liquid mixture into the catalyst-filled fixed-bed reactor, and carrying out reaction to generate the pentadecyl cyclohexane and pentadecyl benzene. The granular solid catalyst Pt/Al2O3 has excellent catalytic activity, catalytic stability and carbon deposit resistance, and is renewable and recyclable. The amount of byproducts and three wastes in the production process is small, and the target product selectivity is higher. The method has higher product yield. The method is simple in production technique and operation, only needs one-step reaction, and thus, is especially beneficial to industrial production.