This paper proposes a method combining space-time coding and mixed-ADC architecture to reduce system power while increasing transmit diversity gain. Meanwhile， this paper analyzes the performance of mixed-ADCs massive MIMO system with space-time coding. By using the additive quantization noise model， we get the expression of the uplink spectral efficiency of the system. And random matrix theory is applied to derive approximate expression. Based on the approximate expression， we further analyze the impact on key system parameters. The simulation result shows that mixed-ADCs architecture can effectively reduce the power and cost of the massive MIMO system with space-time coding， and the transmit diversity gain of the system with space-time coding is double.