Copper calorimeter, based on a calorimetric principle, offers a solution for heat transfer measurement in high enthalpy situation, especially in the erosive flow of high enthalpy shock tunnels. In this study, we numerically investigated the measuring performance of copper calorimeters. Non-ideal effects, such as heat loss to the insulator around and replacement of the average temperature of the copper element by the junction temperature, were discussed in detail. The influences of copper element thickness, copper/constantan wires thickness and sensor diameter were also estimated, with the aim to provide theoretical guidance for the design of copper calorimeter. In addition, corresponding experiments in JF10 high enthalpy shock tunnel were carried out against the data of coaxial thermocouples for verification. Results showed that the non-ideal thermal environment of a copper calorimeter (heat exchange with its surroundings) would result in a smaller measuring heat flux comparing to the one actually loaded; proper thickness of copper element matching the effective test time of shock tunnel was suggested. Besides, preliminary experimental results with corrections showed reasonable agreement with the heat flux of thermocouples, with an average deviation of 8%. Over all, this gauge developed extends and supplements the high enthalpy shock tunnel heat transfer measurements made by other techniques.