The impact of high deposition pressure on the microstructure and incorporation hydrogen impurity within nanocrystalline diamond (NCD) films have been investigated in a home-made microwave plasma chemical vapor deposition (MPCVD) apparatus when the microwave power and the substrate temperature were kept constant at 800W and 650 degrees C, respectively. It is found that high deposition pressure not only influences the grain size and quality, but has conception link with the form and content of the bonded-H incorporated in NCD films. With the deposition pressure increases from 10 kPa to 30 kPa, the average grain size decreases from 33 nm to 13 nm and a large amount of hydrogen is detected in the obtained NCD films by Fourier transform infrared spectroscopy (FTIR). Particularly, the NCD films deposited at 15 kPa possesses the largest amount of the bonded H impurity. The optical emission spectroscopy (OES) from the plasma indicates that the intensity ratio between H alpha and C-2 decreases with the increase of the deposition pressure, which suggests the decline energy levels for the excited H atoms. Based on these experimental results the role of high deposition pressure on the growth of NCD films is discussed.