In the present conditions that prevail in the manufacturing field focuses on supplier retailer coordination. This coordination is very important for inventory management. We can see in our daily life, that inventory also deteriorates with time. Many times, due to uncertain circumstances and sometimes due to technological upgradation, the demand decreases. This article deals with deteriorating inventory due to linearly decreasing and a time-dependent demand over a finite time horizon and variable replenishment intervals. Since there is no considerable amount of study that has been carried out on the problem dedicated to inventory supply chain problems, where the rate of demand decreases with time. In earlier studies increasing demand was discussed by various researchers in comparison to decreasing demand. In this article, a supplier-retailer inventory model for deteriorating items, a linearly decreasing demand (as a function of time), and a finite planning horizon are assumed. Further, a numerical problem is solved and the result is analyses (with the help of Mathematica-12). A sensitivity analysis of parameters is also conducted. [ABSTRACT FROM AUTHOR]