  Topological phase transition is a hot topic in condensed matter physics and
computational material science. Here, we investigate the electronic structure
and phonon dispersion of the two-dimensional (2D) platinum ditelluride
($PtTe_2$) using the density functional theory. It is found that the $PtTe_2$
monolayer is a trivial insulator with an indirect band gap of 0.347eV. Based on
parity analysis, the biaxial tensile strain can drive the topological phase
transition. As the strain reaches 19.3%, $PtTe_2$ undergoes a topological phase
transition, which changes from a trivial band insulator to a topological
insulator with $Z_2=1$. Unlike conventional honeycomb 2D materials with
topological phase transition, which gap closes at K points, the strained
$PtTe_2$ monolayer becomes gapless at M points under critical biaxial strain.
The band inversion leads the switch of the parities near the Fermi level, which
gives rise to the topological phase transition. The novel monolayer $PtTe_2$
has a potential application in the field of micro-electronics.
