•Ternary eutectic mixture of myristic–palmitic–stearic acid (MA–PA–SA) was prepared.•MA–PA–SA/EG (expanded graphite) composite PCM was prepared by pore structures of EG.•Optimum absorption ratio of MA–PA–SA in EG was obtained as 13:1 (by mass).•The prepared MA–PA–SA/EG had a good thermal performance and reliability. Based on theoretical calculation, myristic acid–palmitic acid–stearic acid ternary eutectic mixture (MA–PA–SA) with a mass ratio of MA:PA:SA=52.2:29.4:18.4 was prepared firstly. Then, the MA–PA–SA/expanded graphite (EG) composite phase change material (PCM) with an optimum mass ratio of MA–PA–SA: EG=13:1 was fabricated. The prepared MA–PA–SA and MA–AP–SA composite PCM are characterized by the scanning electron microscope (SEM), Fourier transformation infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetry analyzer (TG). The SEM and FT-IR results showed that the MA–PA–SA was uniformly adsorbed into the network porous structure of EG. The DSC results indicated that the melting and freezing temperatures and latent heats of MA–PA–SA/EG composite PCM were 41.64°C and 42.99°C, and 153.5J/g and 151.4J/g respectively. TG analysis test revealed that the prepared MA–PA–SA/EG composite PCM has a high thermal stability in working temperature range. Thermal cycling test result showed the melting and freezing temperatures and latent heats of the prepared composite PCM changed by 0.28°C and 0.48°C, and −1.63% and −1.32% respectively after 1000 thermal cycles. The thermal conductivity of MA–PA–SA/EG composite PCM was improved by the high thermal conductivity of the EG. All results indicated that the prepared MA–PA–SA/EG composite PCM has proper phase change temperature, high latent heat and thermal conductivity, and good thermal reliability and stability for thermal energy storage in solar heating, waste heating recovery systems and other potential applications.