PHP並沒有真正的多維度陣列，只是Array中的元素可以是Array。

我想你恐怕需要寫一個函數或是類別，用遞迴的方式遍歷陣列元素，來計算出可能的維度。

例如：

<pre class="c" name="code">
<?php
class ArrayDim {
	private $_array;
	private $count=0;

	public $dimension=1;

	function __construct($a) {
		$this->_array = $a;
	}

	function check() {
		$this->check_rec($this->_array);
		return $this->dimension;
	}

	private function check_rec($_a=array()) {
		$this->count++;
		if($this->count>$this->dimension)
			$this->dimension = $this->count;
		foreach($_a as $v) {
			if(is_array($v)) {
				$this->check_rec($v);
			}
		}
		$this->count--;
	}
}
$a = array(array(1,3,5), 3, array(2,4), 4, array(1,array(1,6,4,array(2,4)),8,9));
$b = new ArrayDim($a);
print_r($a);
echo "<br>dimension: ".$b->check();
?>