To research the radiation filed and dose assessment for China HPR1000 nuclear power plant and optimize occupational dose, VISIPLAN code has been utilized for modeling for the reactor vessel head opening. Three dimensional model radiation filed is calculated based on the design source term and PWR experience data. Worker trajectories include maintaining steps, time duration and number of workers. Occupational effective doses are obtained in detail. Results show that the collective dose for reactor vessel head opening is 6.64 mSv. One of the trajectories contributes more than 90% in all the trajectories, upper core component source term contributes 66%, vessel head source term contributes 33%, while other sources contribute little. Methods for dose optimization are recommended based on the characterization of occupational dose. This research provides one way on radiation field study and dose optimization for nuclear facilities radiation protection and dose assessment.