The invention discloses a measurement method for measuring a source end thermal state reflection coefficient. The measurement method comprises the following steps that: S1: utilizing a vector networkanalyzer to carry out calibration on the impedance of a load allocation system; S2: connecting the load allocation system to be between a power source and a load; S3: starting a signal source in the power source, regulating the load allocation system to enable the load allocation system and a power amplifier in the power source to achieve a completely-matched state, and obtaining the input impedance of a dual directional coupler input port in the load allocation system under the completely-matched state; and S4: on the basis of an impendence matching principle, calculating the source end thermal state reflection coefficient.