Though the thermal conductivity of phase change energy storage plasterboard was usually tested by unsteady method, a stable method was proposed to investigate the change of thermal conductivity of phase change energy storage plasterboard. Two testing methods, steady state test method of protection hot plate method and unsteady test method, were compared in the measurement of the thermal conductivity of the phase change energy storage plasterboard with the same proportions. By the analysis and comparison of the two kinds of test methods, the thermal conductivity will decrease with the addition content of phase change materials increasing; both methods can reflect the changes of the thermal conductivity, and the thermal conductivity will be highest if the initial plasterboard temperature is within the phase change temperature interval; the result of thermal conductivity measured by unsteady test method is larger than that of steady test method.