The invention discloses a cross-calibration measurement method for a multi-cavity absolute radiometer. The method is characterized in that a first receiving cavity and a second receiving cavity are subjected to cross calibration; while one receiving cavity receives the light while the other receiving cavity is electrically heated so that thermal equilibrium values of the two receiving cavities areequal, working modes of the two receiving cavities are interchanged, that is, the receiving cavity that originally receives the light is electrically heated, the receiving cavity that is originally electrically heated receives the light, the thermal equilibrium values of the two receiving cavities are again equalized, photoelectric equivalent equations at the two stages are simultaneous, thermoelectric coefficients of temperature sensors of the two receiving cavities are eliminated, and thereby a high-precision irradiance calculation formula is obtained. The method has advantages of excellenttemperature drift inhibition and relatively high measurement precision.