Nitrogen-vacancy center (NV) in diamond has been one of the most powerful quantum sensors, which can achieve ultrahigh sensitivity of electric and magnetic fields due to its long coherence time at ambient condition. However, the quantumness of shallow NVs can be easily destroyed by the interaction between the qubits and their environment, leading to decoherence. In this talk, I will demonstrate the ability of enhancing the coherence of shallow NVs by engineering their local electrostatic environment under ambient condition using a home-made qPlus-based atomic force microscope (AFM). Through the strong local electric field from a sharp tip, we succeeded in manipulating the surrounding electron spin-bath of shallow NVs with nanoscale resolution. Such charge manipulation not only lead to reversible charge-state control of NV center with sub-5nm resolution, but also efficiently suppress its immediate paramagnetic noise, yieling an up to 20-fold enhancement of spin-echo time (T2). The optimized NV center realized a sensitivity even up to single proton spin. Our techniques pave the way for understanding the decoherence mechanism of shallow solid-state qubits and defeating its fundamental limitation on quantum sensing.