In grey network planning, the parameters of duration are expressed as interval grey numbers. When the time parameters were calculated according to grey number operational laws, grey degree of the results is expanded unnecessarily and sometimes the lower bounds are negative. So, the time parameters of grey network planning lost the original meaning. The present paper studies on the time parameters of grey network planning further by adjusting the time parameters according to their practical meaning. This method can solve the problems above. It enhances the flexibility and applicability in decision-making and has important significance for project managers.