  SS433 is an extraordinary X-ray binary which is ejecting bipolar jets with
$26\%$ of the speed of light. Associated with the supernova-like shell W50,
SS433 is also probably one of the youngest X-ray binaries with an age of
$\lesssim 10^5$ yr. However, the masses of the two components in SS433 and even
the nature of the compact object are still under debate. In this work, assuming
that the compact object is a black hole, we employ a binary population
synthesis method to study the formation of SS433. We use previous estimates of
the age of W50 and the duration of the jet activity to constrain the
evolutionary history. Our calculations suggest that SS433 likely harboured a
Hertzsprung gap star at the beginning of the current Roche-lobe overflow phase.
The masses of the black hole and the optical/donor star in SS433 suggested by
the simulations are around $8\ M_{\odot}$ and $24\ M_{\odot}$, respectively.
Future measurement of the donor mass and radius can help infer not only the
orgin of the binary but also the nature of the nebula W50.
