Miniaturized electron cyclotron resonance (ECR) ion sources are widely used in compact ion implanters, miniature neutron tubes, and miniaturized ion thrusters. To understand the mechanism of miniaturized ECR ion sources, a miniaturized deuterium ion source developed by Peking University is taken as the research object. In this work, a global model based on particle balance equations is developed for hydrogen and deuterium plasma research inside the miniaturized ECR source. The research results show that both the hydrogen discharge process and the deuterium discharge process of the ion source have strong dependences on the gas pressure and microwave power. The calculated results show that high power is beneficial to increase the ratio of H⁺ (D⁺) ions, low pressure is helpful to increase the ratio of H₂⁺ (D₂⁺) ions, high pressure and low power are beneficial to increase the ratio of H₃⁺ (D₃⁺) ions. In addition, there are large differences between the ion ratios of hydrogen discharge and deuterium discharge. Under the same operating parameters, the ratios of D⁺ ions are 10%~25% higher than the ratios of H⁺ ions since the plasma density of deuterium discharge is higher than that of hydrogen plasma. Therefore, during the operation of miniaturized source, H₂ gas can be used instead of D₂ gas to carry out experiments, and a quantitative estimate of the ratio of D⁺ ions under the corresponding operating parameters can be given based on the ratio of H⁺ ions. At last, the calculated results show that high microwave power is a prerequisite for high ratio of H⁺ (D⁺) ions. However, due to the limitation of microwave coupling efficiency, the miniaturized ECR ion source cannot work in the region where the microwave power is greater than 150 W, so that the H⁺ (D⁺) ratio cannot be further increased, which limits its further applications in neutron sources, implanters and etc. Therefore, how to improve the microwave coupling efficiency should be one of the key research contents of the miniaturized ECR ion source. The global model proposed in this paper is helpful to understand the physical process of the miniaturized ECR ion source, but there are also some shortcomings. Firstly, the influence of the secondary electron emission coefficient is not considered in the model, so it is impossible to study the influence of wall materials on ion ratio in detail. Secondly, since the dissociation degree depends on the results of plasma diagnosis, and the error of plasma diagnosis will have a certain impact on the accuracy of the model. In addition, only the models of hydrogen and deuterium plasma are established in this paper, thus it is impossible to study the process of more gas discharge plasma. In the future, the above factors will be considered and the model will be further improved to establish a complete and self-consistent global model of the miniature ECR ion source.