  A recent experiment has reported the first observation of a zero-field
fractional Chern insulator (FCI) phase in twisted bilayer MoTe$_2$ moir\'e
superlattices [Nature 622, 63-68 (2023)]. The experimental observation is at an
unexpected large twist angle 3.7$^\circ$ and calls for a better understanding
of the FCI in real materials. In this work, we perform large-scale density
functional theory calculation for the twisted bilayer MoTe$_2$, and find that
lattice reconstruction is crucial for the appearance of an isolated flat Chern
band. The existence of the FCI state at $\nu = -2/3$ are confirmed by exact
diagonalization. We establish phase diagrams with respect to the twist angle
and electron interaction, which reveal an optimal twist angle of $3.5^\circ$
for the observation of FCI. We further demonstrate that an external electric
field can destroy the FCI state by changing band geometry and show evidence of
the $\nu=-3/5$ FCI state in this system. Our research highlights the importance
of accurate single particle band structure in the quest for strong correlated
electronic states and provides insights into engineering fractional Chern
insulator in moir\'e superlattices.
