  Recently, $\beta$-Te (atomically 2D tellurium) with rectangular crystal
structure has been synthesized successfully on highly oriented pyrolytic
graphite substrates by using molecular beam epitaxy. It has been found
possessing remarkable properties such as ultralow lattice thermal conductivity
and high thermoelectric efficiency. Based on the first-principles calculations,
we study the thermal expansion and thermomechanic properties of the
experimental phase monolayer $\beta$-Te, using quasiharmonic approach. It is
found $\beta$-Te shows large positive thermal expansion at elevated
temperature, while the linear thermal expansion coefficient is negative along a
direction at very low temperature. The linear thermal expansion coefficient
along b direction is 4.9*10$^{-5}$ K$^{-1}$ at 500 K, which is considerably
large in 2D materials. $\beta$-Te exhibits strong in-plane anisotropy,
including thermal expansion, 2D elastic moduli and Poisson's ratios. However,
the elastic moduli, Poisson's ratios and the in-plane anisotropy are weakened
with increasing temperature, and the variations are dominated by the
generalized mode Gr\"{u}neisen parameters.
