In this paper, we used molecular dynamics to simulate dynamic properties and micro-structure of the water-hydrazine particle system under various conditions:chamber condition of 1 atm, 298 K; pressurized water reactor (PWR) environment of 155 atm, 626 K; with number of water molecules of 256, numbers of hydrazine (N2H4) molecules of 0, 25, 50 and 75. And we have also explored the impact on the dissolved oxygen in water when hydrazine molecule is added to the system. The simulation results show that in the chamber ambient, when the number of molecules of hydrazine varies from 0 to 25, 50 and 75, the mean square displacement (MSD) in the particle system will increase with the number of particles of the hydrazine. The MSD for hydrazine molecule of number 0 will be ten less than that of 25, 50 and 75. Under the PWR environment, with hydrazine molecule number of 50, the MSD is about 4 times higher than that in chamber ambient. At the same time, under such condition, the MSD of particle system does not increase with the number of hydrazine molecules. The MSD with hydrazine molecule of 50 is higher than its counterpart with the number of molecules of 25 or 75. In addition, the micro-structure of particle systems, from the perspective of the radial distribution functions (RDF), will increase with the increase of concentration of hydrazine in chamber ambient. This conclusion goes along with the fact that hydrazine is easy to react with water to generate hydrazine hydrate. While in the pressurized water reactor environment, the radial distributions of the water with the number of hydrazine molecules of 25, 50 and 0 will have no big change. But the radial distributions with the number of hydrazine molecules of 75 increase significantly. It can be seen from simulation data that hydrazine added to PWR significantly inhibits the dissolved oxygen in water, but the inhibition does not increase in proportion to the increase of the concentration of hydrazine. This phenomenon and its causes are revealed comprehensively in this paper.