The usual semi-active control algorithms are determining the optimal control force based on structure feedbacks of displacement and velocity responses. But in actually, these strategies lead to negative affect to controlling effect, because of difficulties of measurement of displacement and velocity responses, data transmission and line layment. This paper puts forward a new discrete control algorithm based on inter-storey displacement and inter-storey velocity responses. The inter-storey displacement could be measured precisely by displacement meter attached to magnetorheological damper, while the inter-storey velocity could be obtained by differential inter-storey displacement, then the control force of the damper in this storey could be determined independently. The results of the numerical analysis illustrate that the proposed control algorithm have good damping effects in the earthquake.