Proton exchange membrane fuel cell (PEMFC) generates substantial waste heat during operation. Excessive temperature induces performance degradation and may cause irreversible cell damage. To address the non-uniform temperature distribution in PEMFCs, this study proposes a novel composite cooling channel that, for the first time, integrates a fluid oscillator with a bionic leaf-inspired cooling structure. Unlike conventional parallel or biomimetic channels that rely on steady flow distribution, the introduced fluid oscillator generates self-induced oscillating jets that dynamically modify the coolant flow within the bionic branches. Experimental results demonstrate that this coupling mechanism significantly enhances coolant mixing and heat transfer, resulting in superior temperature uniformity compared with both traditional parallel channels and standalone bionic leaf cooling channels. The results show that the cooling fluid distribution and temperature uniformity of the composite cooling channel are better than those of the parallel cooling channel and the bionic leaf cooling channel. The maximum temperature decreases from 348.45 K to 346.28 K, the temperature difference decreases from 3.62 K to 2.13 K, and the temperature uniformity index decreases from 1.53 to 0.49, which is 68.0% lower than that of the parallel cooling channel. Compared with the serpentine cooling channel, the compound cooling channel effectively solves the problem of excessive pressure drop while ensuring efficient cooling performance. The pressure drop of serpentine cooling channel is 28218.34 Pa, while that of compound cooling channel is only 1477.28 Pa, which is 94.8% lower. Further parameter optimization of the fluidic oscillator reduced the pressure drop to 1347.72 Pa and improved the temperature uniformity index to 0.41.