  Out of time ordered correlator (OTOC) is recently introduced as a powerful
diagnose for quantum chaos. To go beyond, here we present an analytical
solution of OTOC for a non-chaotic many body localized (MBL) system, showing
distinct feature from quantum chaos and Anderson localization (AL). The OTOC is
found to fall only if the nearest distance between the two operators being
shorter than $\xi\ln t$, where $\xi$ is dimensionless localization length.
Thereafter, we found an universal power law decay of OTOC as $2^{-\xi\ln t}$,
implying an universal logarithmic growth of second R\'{e}nyi entropy, where
$\xi$ plays the role of information scrambling rate. A relation between
butterfly velocity and scrambling rate is found.
