var grid = new Ext.grid.GridPanel({
			bodyStyle:'width:100%',
			store: store,
			columns: columns,
			stripeRows: true,
			autoScroll:true,
			height:document.body.clientHeight-Ext.get('gridarea').getTop(),
			viewConfig:{
					forceFit: false,
					sortAscText: "升序排序",
    			sortDescText: "降序排序",
					columnsText:'顯示列'
			},
			bbar:new Ext.PagingToolbar({
			store: store
			})
 

然後是監聽窗體大小

//視窗大小改變觸發
		window.onresize=function(){
			grid.setWidth(document.body.clientWidth);
			grid.setHeight(document.body.clientHeight-Ext.get('gridarea').getTop());
		}