For electromagnetic environment complex evaluation,a novel evaluation method was proposed based on S-transform and probabilistic neural network (PNN). S-transform was applied to perform time-frequency analysis on the electromagnetic environment disturbance samples,the evaluation parameters such as time occupation,frequency occupation and energy occupation of the samples were extracted synchronously,physical interpretation of each parameter was analyzed,and the calculation formulas of them were shown. At the same time,frequency coincidence,modulation similarity and background noise intensity were selected as important evaluation indicators. These parameters were then used to train a PNN which was adopted to evaluate environmental complexity. The simulation results show that the proposed method has integrity of parameter extraction and relatively high evaluation accuracy,and it can also give excellent evaluation for high level noises background and small training set.