If you have a loan of 650,000 yuan with a term of 30 years, and you want to pay off 100,000 yuan in 4 years, you can reduce your loan by up to about 19,741.67 yuan per month.

The calculation here is based on the reduction in monthly payments, as well as the interest rate on the loan. Depending on the interest rate of the loan, the monthly payment will vary.

First, with the same interest rate, you can reduce the loan amount every month to pay off the $100,000 in 4 years. In this way, you can reduce your loan by approximately 19,741.67 yuan per month.

Secondly, you can change the interest rate on your loan so that you can reduce your loan amount by more each month. If you're able to get a lower interest rate, the amount you can reduce on your loan each month will be greater.

Finally, you may also consider prepayment to pay off the loan faster in a short period of time. Paying off your loan early can reduce your loan amount, allowing you to pay off more of your loan every month.

In summary, if you have a loan of $650,000 with a term of 30 years and you want to pay off $100,000 in 4 years, you can reduce your loan by up to about $19,741.67 per month . Additionally, you might consider changing the interest rate on your loan, or paying it off early so that you can reduce your loan amount by more each month.