  We report spectral analysis of the persistent black hole X-ray binary, 4U
1957+115, using AstroSat, Swift and NuSTAR observations carried out between
2016-2019. Modelling with a disk emission, thermal comptonization and blurred
reflection components revealed that the source was in the high soft state with
the disk flux $\sim 87$ % of the total and high energy photon index $\sim2.6$.
There is an evidence that either the inner disk radius varied by $\sim25$ % or
the colour hardening factor changed by $\sim12$ %. The values of the inner disk
radius imply that for a non-spinning black hole, the black hole mass is $<7$
M$_\odot$ and the source is located $>30 $ kpc away. On the other hand, a
rapidly spinning black hole would be consistent with the more plausible black
hole mass of $< 10$ M$_\odot$ and a source distance of $\sim10$ kpc. Fixing the
distance to $10$ kpc and using a relativistic accretion disk model, constrained
the black hole mass to 6 M$_\odot$ and inclination angle to 72$^{\circ}$. A
positive correlation is detected between the accretion rate and inner radii or
equivalently between the accretion rate and colour factor.
