Thank U, i find the way to change it
In moodle 1.9 you can see
file: index.php
...
// Bounds for block widths
// more flexible for theme designers taken from theme config.php
$lmin = (empty($THEME->block_l_min_width)) ? 100 : $THEME->block_l_min_width;
$lmax = (empty($THEME->block_l_max_width)) ? 210 : $THEME->block_l_max_width;
$rmin = (empty($THEME->block_r_min_width)) ? 100 : $THEME->block_r_min_width;
$rmax = (empty($THEME->block_r_max_width)) ? 210 : $THEME->block_r_max_width;
...
So I add
file theme/my_theme/config.php
...
$THEME->block_l_min_width = 210;
$THEME->block_l_max_width = 210;
$THEME->block_r_min_width = 210;
$THEME->block_r_max_width = 210;