The BiFeO3/g-C3N4 heterostructure, which is fabricated via a simple mixing–calcining method, benefits the significant enhancement of the pyrocatalytic performance. With the growth of g-C3N4 content in the heterostructure pyrocatalysts from 0 to 25％, the decomposition ratio of Rhodamine B (RhB) dye after 18 cold-hot temperature fluctuation (25-65 ℃) cycles increases at first and then decreases, reaching a maximum value of ～94.2％ at 10％ while that of the pure BiFeO3 is ～67.7％. The enhanced dye decomposition may be due to the generation of the internal electric field which strengthens the separation of the positive and negative carriers and further accelerates their migrations. The intermediate products in the pyrocatalytic reaction also have been detected and confirmed, which proves the key role of the pyroelectric effect in realizing the dye decomposition using BiFeO3/g-C3N4 heterostructure catalyst. The pyroelectric BiFeO3/g-C3N4 heterostructure shows the potential application in pyrocatalytically degrading dye wastewater.