Aiming at the wavefront detection without an ideal point beacon in the adaptive optical system under the strong turbulent environment, we proposed a method to detect the optical field information of extended beacons using a Plenoptic sensor. The optical field imaging principle, wavefront phase reconstruction algorithm, and error influence rule of extended beacons were studied. The imaging process of the extended beacon on the optical field sensor was simplified through the equivalence method, and the optical field images were rearranged in a specific way. The image cross-correlation and Zernike mode methods were used to realize the wavefront reconstruction of the 0° field of view. Simulation studies were conducted on error-influencing factors such as different input aberration coefficients, the number of single-row microlens elements, and noise. The results show that when the input aberration is less than 6.5 λ, the wavefront reconstruction accuracy is about 0.08 λ. For the image detector with an image resolution of 1080×1080 and pixel size of 5.5 μm, the wavefront reconstruction accuracy is the highest when the number of single row microlens units is between 40 and 50, and the system noise hardly affects the accuracy. Finally, an extended beacon wavefront detection system was built to reconstruct the four aberrant wavefronts of 0° field of view by detecting the extended beacon. The wavefront reconstruction accuracy of the experimental system is about 0.04 λ, which meets the wavefront detection requirements of the adaptive optical system.