Monocular depth estimation, which provides a critical method for understanding 3D scene geometry, is an ill-posed problem. Recent research studies have achieved significant progress by reliable network architecture and optimized constraints, such as spatial propagation network and depth metrics. We propose an effective generative adversarial network for fast and accurate monocular depth estimation. Our approach demonstrates the feasibility of applying a dense-connected UNet for reducing information transmission loss and then fine-tuning the blur depth by the high-order convolutional spatial propagation network (CSPN) that used a modified loss function of discriminator. Furthermore, we modify the loss function of discriminator by adding the correlation loss that is used to measure the similarity of real and fake labels. Compared with the original CSPN, the high-order CSPN reduces the computation complexity and accelerates the convergence of the generator network by increasing the order of kernel, which emphasizes the weight of kernels in the update formula. With these modifications, our generative adversarial second-order convolutional spatial propagation network (GA-CSPN) achieves more accurate results against state-of-the-art methods in both indoor and outdoor scenes on Make3D, KITTI 2015, and NYUv2 datasets.