  We report the results from \textit{AstroSat} observations of the transient
Galactic black hole X-ray binary MAXI J1535-571 during its hard-intermediate
state of the 2017 outburst. We systematically study the individual and joint
spectra from two simultaneously observing \textit{AstroSat} X-ray instruments,
and probe and measure a number of parameter values of accretion disc, corona
and reflection from the disc in the system using models with generally
increasing complexities. Using our broadband ($1.3-70$ keV) X-ray spectrum, we
clearly show that a soft X-ray instrument, which works below $\sim 10-12$ keV,
alone cannot correctly characterize the Comptonizing component from the corona,
thus highlighting the importance of broadband spectral analysis. By fitting the
reflection spectrum with the latest version of the \textsc{relxill} family of
relativistic reflection models, we constrain the black hole's dimensionless
spin parameter to be $0.67^{+0.16}_{-0.04}$. We also jointly use the reflection
spectral component (\textsc{relxill}) and a general relativistic thin disc
component (\texttt{Kerrbb}), and estimate the black hole's mass and distance to
be $10.39_{-0.62}^{+0.61} M_{\odot}$ and $5.4_{-1.1}^{+1.8}$ kpc respectively.
