  We use the In data collected during the 2019 outburst from X-ray pulsar 4U
1901+03 to complement the orbital parameters reported by Fermi/GBM. Using the
Insight-HXMT, we examine the correlation between the derivative of the
intrinsic spin frequency and bolometric flux based on accretion torque models.
It was found that the pulse profiles significantly evolve during the outburst.
The existence of two types of the profile's pattern discovered in the
Insight-HXMT data indicates that this source experienced transition between a
super-critical and a sub-critical accretion regime during its 2019 outburst.
Based on the evolution of the pulse profiles and the torque model, we derive
the distance to 4U 1901+03 as 12.4+-0.2 kpc.
