Nitrogen-vacancy (NV) centers in diamond are suitable sensors of high-sensitivity magnetometry, which have attracted much interest in recent years. Here, we demonstrate sensitivity-enhanced ensemble magnetometry via adaptively complete transitions overlapping with a bias magnetic field equally projecting onto all existing NV orientations. Under such conditions, the spin transitions corresponding to different NV orientations are completely overlapped, which will bring about an obviously improved photoluminescence contrast. We, furthermore, introduce particle swarm optimization into the calibration process, to generate this bias magnetic field automatically and adaptively using computer-controlled Helmholtz coils. By applying this technique, we realize an ∼1.5 times enhancement and obtain a magnetic field sensitivity of 855pT/Hz by utilizing a group of completely overlapped transitions, compared to the 1.33nT/Hz obtained utilizing a single transition in continuous-wave magnetometry. Our approach can be conveniently applied in direction-fixed magnetic sensing and to obtain the potentially maximum sensitivity of ensemble-NV magnetometry.