Focused light field imaging has overcome the disadvantages of low spatial resolution in traditional light field imaging, but the induced artifacts at out-of-focus planes due to sacrificing the angle sampling density. This not only affects the visual appearance of the image but also severely decreases the accuracy of defocus response analysis. We present a method based on sliding window fusion and adaptive median filtering, which can improve the angle resolution and eliminate the artifacts at out-of-focus planes. A window with an appropriate size is selected to slide in the sub-images of the four-dimensional light field data with a specific step. Basic light field refocusing algorithm is conducted on each slide to produce multi-view data, which are then fused to get a refocused image at a corresponding plane. The focal stack can be obtained by changing the window size and repeating the above calculation. Each layer of the focal stack is filtered by an adaptive median filter with the kernel size being linearly correlated with the window size. As a result, artifacts can be removed in the whole focal stack. Todor dataset is used to test the proposed method. The results show that the proposed method improves the visual appearance at out-of-focus planes, and the accuracy of defocus response.