Abstract: Based on measuring the pressure increment of liquid that results from heating by the absorbed microwave energy, a calorimeter with pressure sensor is designed. Pure water is used as the absorbing material. The calorimeter has advantages of less requirements on the thermodynamic parameters of liquid, wide measurement range and high sensitivity. The experimental results indicate that the calorimeter can be used to measure pulsed microwave energy, and the energy resolution and measurement range of which are 0.5 J and 180 J, respectively. Meanwhile, with careful electromagnetic simulation of calorimeter cavity, the calorimeter can also be used to measure the high power microwave energy.