Abstract: In order to understand the physical mechanism, transient processes and spatial distribution of the microwave electron cyclotron resonance (ECR) plasma profoundly, a typical emission spectrum obtained from the nitrogen ECR plasma by a grating monochrometer has been studied, and the plasma density distribution in the reaction chamber and the influence of discharge pressures on it were also diagnosed using a double Langmuir probe. The results demonstrate that there mainly exist excitation collisions, ionizing collisions and dissociation collisions in the nitrogen ECR plasma, and the dominating reactive species are high excited nitrogen molecular ions. Under the influence of magnetic field, the ECR plasma in the upstream region has poor uniformity distribution, whereas the plasma in the downstream region, under the influence of the plasma density gradient, takes on the homogeneous distribution. And the discharge pressure has a best value (p=0.07Pa) with a fixed microwave power (Pw=400W).