array(
    [0] = array(
        ['a'] = 323,
        ['b'] = array(
            ['b1'] = 1
            )
        )    
    [1] = array(
        ['a'] = 234,
        ['b'] = array(
            ['b1'] = 1
            )
        )
    [2] = array(
        ['a'] = 135,
        ['b'] = array(
            ['b1'] = 2
            )
        )
)

<?php
function cmp($a,$b){
    return $a['b']['b1'] == $b['b']['b1']?($a['a'] - $b['a']):($a['b']['b1'] - $b['b']['b1']);
}

$array = array(0=>array('a'=>323,'b'=>array('b1'=>1)),
               1=>array('a'=>324,'b'=>array('b1'=>1)),
               2=>array('a'=>135,'b'=>array('b1'=>2)),
);

usort($array,'cmp');
var_export($array);

------解决方案--------------------
探讨

这意思？

PHP code
<?php
function cmp($a,$b){
    return $a['b']['b1'] == $b['b']['b1']?($a['a'] - $b['a']):($a['b']['b1'] - $b['b']['b1']);
}

$array = array(0=>array('a'=>323,'b'=>array('b1'=>1)……