Most quantitative magnetic resonance imaging (qMRI) techniques remain time-consuming and sensitive to motion, especially when large volume imaging is needed. Simultaneous multi-slice (SMS), which is not restricted by single-slice evolution time, is an acceleration method for MRI. Here we propose a flexible SMS T2 mapping method based on overlapping echo detachment (OLED) planar imaging. Experimental results demonstrate the superior performance of our method. Reliable multi-slice T2 maps can be obtained in a single shot within milliseconds for the first time.