你已经吧对象转成字符串了

var data1 = {
                "raster_metainfo": [0,0,0,0,0,0,0],
                "navigation_metainfo": [0,0,0,0,0,0,0],
                "thematic_metainfo": [0,0,0,0,0,0,0],
                "text_metainfo":  [0,0,0,0,0,0,0],
                "video_metainfo":  [0,0,0,0,0,0,0],
                "database_metainfo": [0,0,0,0,0,0,0],
                "service_metainfo":  [0,0,0,0,0,0,0]
            };
            var a ='navigation_metainfo';
            console.log(data1.a);
            console.log(data1[a]);

你这么写肯定不对啊，编译成的是data1里面的a，但是data1.a根本不存在，写成这样就行了：
console.log(data1[a]);

var data1 = {
                "raster_metainfo": [0,0,0,0,0,0,0],
                "navigation_metainfo": [0,0,0,0,0,0,0],
                "thematic_metainfo": [0,0,0,0,0,0,0],
                "text_metainfo":  [0,0,0,0,0,0,0],
                "video_metainfo":  [0,0,0,0,0,0,0],
                "database_metainfo": [0,0,0,0,0,0,0],
                "service_metainfo":  [0,0,0,0,0,0,0]
            }


               console.log(data1.navigation_metainfo);    //这个是可以取到整个navigation_metainfo 的数组
                             console.log(data1.navigation_metainfo[0]); //这个可以取到数组中的值，我这里取得是第一个值。

这里的 a 是一个变量，不能直接 .a 可以通过data1 [a] 获取这个属性值。