A dynamic model for high voltage Child-sheath of mixed multi-component plasmas is built up, and the characteristics of high voltage Child-sheath of mixed D⁺ and Ti²⁺ plasmas is numerically studied. The theoretical and numerical results demonstrate as follows. The depth of Child-sheath will increase and electric field intensity on target will decrease by increasing the ratio of D⁺ to Ti²⁺, decreasing the sheath-entering velocity of D⁺ or Ti²⁺, and decreasing the density of mixed plasmas. Through the above ways, ions could achieve convergent transportation and breakdown risk on target could also be reduced. As the increase of accelerating voltage, the range of stable ion-extraction operating region will firstly increase and then decrease. By increasing the ratio of D⁺ to Ti²⁺ and decreasing the sheath-entering velocity of D⁺ or Ti²⁺, the range of stable ion-extraction operating region could be notably increased.