This research work presents the multiply optimizing to minimize surface roughness and maximize cutting speed (Vc) when Electrical Discharge Machining (EDM) hardened 90CrSi steel. The input parameters used to investigate their effects on the responses are purposely selected such as Concentration of powder, Pulse on time, Pulse off time, Current, and Voltage. Grey Relational Analysis (GRA) is combined with Taguchi method to find the optimal set of machining parameters which can satisfy the responses. The results show that Pulse off time has the smallest effects (2,03%) but Current has the strongest influence (32,29%) on the grey grade value. The proposed model corfirmed by experiment and ANOVA exhibited the reability approche to predict surface roughness and material removal rate.