The invention relates to a carbon/graphene flexibility strain sensor and a preparation method thereof. The preparation method comprises the steps of firstly preoxidizing and carbonizing polyacrylonitrile/graphene composite nanometer fiber yarns to obtain carbon/graphene composite nanometer fiber yarns; and then compounding the carbon/graphene composite nanometer fiber yarns with an elastic film prepared from thermoplastics polymer, a lead and a conductive adhesive to obtain the carbon/graphene flexibility strain sensor. The preparation method is reasonable in preparation process; the sensor issteady in performance in the preparation process and the dimension of the sensor can be adjusted based on demands; the sensitivity coefficient of the obtain carbon/graphene flexibility strain sensoris 400-2500 when the sensitivity coefficient is A; and when the circular stretching is carried out in the presence of the elongation from 0 to A, the total test time is 2000s and the cycle index is 28, the standard deviation of the sensitivity coefficient is 0.5% to 4%; and A is equal to 1.5% t 2.3%.