The measurement of the radiation field is a unique method for high-power microwave power measurement. Since the radiation field of electromagnetic waves has a strict mathematical expression, power measurements at one or multiple points in the radiation field can be used to proportionally determine the power of the entire electromagnetic field through the mathematical expression. This chapter introduces various methods and computational techniques for radiation field power measurement, including the total attenuation measurement method, single-point measurement method, multi-point measurement method, numerical integration method, and fitting method et ct. Additionally, it provides the calibration methods for various parameters used in the measurements.