Abstract: This paper proposes a new method for measuring the high heat flux of a long duration. The heat sink is made of phase change materials (PCMs) and metal honeycomb materials with high thermal conductivity. The PCMs, with high latent heat, are used to absorb the heat continuously, which is received by the heat flux meter, then the heat flux as high as 1 MW·m^-2 can be measured for a duration longer than 2000 s. An apparent heat capacity method is adopted to establish the analytical model for the measurements of high heat flux of a long duration. The model is validated by the experimental results and is used to study the influence of the physical properties of PCMs on the measuring method. The physical parameters include the thermal conductivity, the phase change latent heat and the phase transition temperature. It is shown that phase change material of higher heat sink thermal conductivity, lower phase transition temperature higher than the initial environmental temperature, and larger latent heat is suitable for measuring high heat flux of a long duration.