[en] A rapid thermal response composite phase change material (PCM) is prepared by absorbing paraffin into expanded graphite, which is of excellent absorbability. The highest thermal conductivity of the composite samples can reach 4.676 W m^-1 K^-1. The prepared composite PCM has excellent thermal storage performance and its heat storage period and heat release period are shortened 65.3% and 26.2%, respectively, compared with that of the paraffin. Applying the composite PCM to an electronic device's heat sink can effectively improve the performance of resisting the shock of high heat flux and ensure the reliability and operating stability of electronic and electrical equipment. The experimental results show that the apparent heat transfer coefficients of the experimental heat sink with the PCM are 1.36-2.98 times higher than those of the heat sink without the PCM. Based upon the quadratic equation, the total relative uncertainty of the experimental system is estimated that |(δk)/k |<2.8%