Problem of soft starter for new replaced pump & motor

Question: we've been using soft starter for pump motor set up for 8 years, why the starting current goes high recently when we replaced new set of pump?

You may have any of a number of issues:

The new pump may be able to deliver slightly higher pressure than the old one, so it may require slightly more power than the previous one.
The new motor may have higher efficiency than the old one. This will often be coupled with a slightly higher starting current requirement.
Your new motor has a slightly lower nominal FLC, so most likely it is also designed to operate at a slightly lower slip than the old one. If the driven pump is of the same design as the old one, this may lead to higher power uptake for the motor/pump assembly. - I have seen this issue more than once in practice, when the pump manufacturer did not change the pump when he changed to a more efficient motor.
If your soft starter attempts to keep the starting voltage down for too long, then the starting current remains relatively high for too long, causing overheating of the motor windings.
The output current from the Soft Starter is far from sinusoidal, and the high harmonics content causes additional copper (and iron) losses, without contributing to the produced starting torque.
If this pump operates in parallel with other pumps, it may be that it takes over a large part of the load as a result of a slightly higher discharge pressure, and therefore it can become overloaded.
If your soft starter has been in service for a number of years, it may need re-commissioning with the new motor (it may not be able to automatically sense any change, and act on it of its own accord). You may have to manually enter new parameters, or set it into some "commissioning" mode for that to happen.

You should firstly verify that the new pump has been installed electrically correctly. After that you should record both process parameters and electrical parameters. Flow and pressure increase across the pump, preferably also absolute pressures and temperatures, so you can eliminate pump cavitation etcetera as part of your problem, actual pump speed (RPM) and all relevant electrical parameters, such as voltage and current both during start up and during steady state run. You should then check that the soft starter actually closes its bypass contactor as soon as the pump is up to speed.

If I were you, I would also do a couple of DOL starts of the pump, just to see if the soft starter is really required. If you do not experience too much of a flicker when starting this little pump, I would then simply remove the Soft Starter.