Because the sum of digits divisible by 9 must be divisible by 9,

So the selected three numbers meet the following three conditions:

(1), (9,8, 1), (7,6,5), (4,3,2), and the largest three digits are 98 1, 765,432;

(2), (9, 7, 2), (8, 6, 4), (5, 3, 1), then the largest three digits are 972, 864, 531;

(3), (9, 5, 4), (8, 7, 3), (6, 2, 1), and the largest three digits are 954,873,621;

According to the "approximation principle", when the sum of each number is constant, the closer the factors are, the greater the product is.

Therefore, the maximum multiplication formula of the three-digit product is: 954×873×62 1,

So the answer is: 954× 873× 62 1.