  Recently a general prescription for determining the vacuum modular flow
generator and the corresponding modular Hamiltonian in the BMS-invariant field
theories (BMSFTs) have provided by Apolo et. al \cite{Apolo}. According to this
paper Einstein gravity in asymptotically flat three-dimensional spacetimes is
dual to a BMSFT. In the present paper we extend this study to the generalized
minimal massive gravity model (GMMG). So we study some aspects of
$Flat_3/BMSFT$ holography in the framework of this model. We derive the modular
Hamiltonian for single intervals in thermal and non-thermal BMSFTs and show its
holographic dual is the gravitational charge associated with isometries that
preserve the asymptotic form of the metric. Also using the modular Hamiltonian
we derive the first law of entanglement entropy. Our results for GMMG model
reduces to the result for Einstein gravity in $2+1$ dimension, when $\mu , m^2
\to \infty $, and $\sigma=-1$. These limiting cases, are a place in parameter
space of model, where GMMG model reduces to the Einstein gravity.
