The afterglow properties of long afterglow luminescent materials are greatly affected by their defects, which are distributed on the grain surface. Increasing the exposed surface area is an important method to improve the afterglow performance. In this research, long rod‐shaped long afterglow materials Sr2MgSi2O7:Eu2+,Dy3+ were prepared using the hydrothermal‐coprecipitation method. When the reaction time reached 96 h, the length of the afterglow materials could grow to 2 mm, and the sintering temperature was just 1150°C. The emission spectra of all obtained samples upon excitation at 397 nm had a maximum of 465 nm, which belonged to the representative transition of Eu2+. The initial brightness was 1.35 cd/m2. The afterglow time could reach 19 h, giving a good afterglow performance. The research on this kind of material has essential significance in the exploration of luminescence mechanisms and their applications.