Multiple attribute group decision-making (MAGDM) has become an emerging research area. How to determine the weights of experts is a fundamental topic. This paper presents a novel approach with a rough set group method, to determine the weights of decision makers (DMs), in which the decision information of each decision maker (DM) is expressed by a matrix of interval numbers. In this paper, we firstly build a lower rough group decision (LRGD) and an upper rough group decision (URGD) based on the rough group decision. Then we define a Lower positive ideal solution (Lower PIS) as the average matrix of LRGD and Upper positive ideal solution (Upper PIS) as the average matrix of URGD. The PIS is the average matrix of Lower PIS and Upper PIS, meanwhile, the negative ideal solution (NIS) has the maximum separation from positive ideal solution. After that, we define the weight of each DM by distances from DM’s decision to PIS and NIS. Finally, an example “air-quality monitoring stations” is provided to illustrate the calculation process of the proposed approach in details.