The high spatial search complexity of the direct positioning method in passive positioning systems leads to long positioning time and high computational resource consumption. In response to this issue, this article proposes a fast localization scheme based on composite convolutional neural networks (CCNN), which can effectively explore the correlation between the position of the radiation source and the characteristics of the received signal. CCNN is a 20‐layer composite network based on fully convolutional network layer, which is composed of convolutional layers, batch normalization (BN) layers, and ReLU activation function layers with unidirectional connections. Then, CCNNs are adjusted and trained for positioning single and multiple radiation sources, respectively. Simulation results show that the computational time of the proposed method can be reduced by nearly 98% compared with the direct positioning scheme. Meanwhile, about 71.2% of positioning error's reduction is achieved.