为什么json警报数据返回Undefined

after the alert(JSON.stringify(ort_list));
I'm getting output like this.

[{"status":"success","result":{"BUNDESLAND_NAME":"Rheinland-Pfalz","KREIS_TYP":"Landkreis","GEMEINDE_NAME":"Aach","GEMEINDE_LAT":"4978960","GEMEINDE_LON":"659052","ID_0":"2","ORT_NAME":"Aach","ORT_LAT":"4978972","ORT_LON":"659055","PLZ":"54298"}}]

now I want to get the alert value of BUNDESLAND_NAME how could I get that.

Use this:

var data = [{"status":"success","result":{"BUNDESLAND_NAME":"Rheinland-Pfalz","KREIS_TYP":"Landkreis","GEMEINDE_NAME":"Aach","GEMEINDE_LAT":"4978960","GEMEINDE_LON":"659052","ID_0":"2","ORT_NAME":"Aach","ORT_LAT":"4978972","ORT_LON":"659055","PLZ":"54298"}}];
alert(data[0].result.BUNDESLAND_NAME);

or directly, based on your code

alert(ort_list[0].result.BUNDESLAND_NAME);

assume

ort_list = [{"status":"success","result":{"BUNDESLAND_NAME":"Rheinland-Pfalz","KREIS_TYP":"Landkreis","GEMEINDE_NAME":"Aach","GEMEINDE_LAT":"4978960","GEMEINDE_LON":"659052","ID_0":"2","ORT_NAME":"Aach","ORT_LAT":"4978972","ORT_LON":"659055","PLZ":"54298"}}];

<?php

$data='[{"status":"success","result":{"BUNDESLAND_NAME":"Rheinland-Pfalz","KREIS_TYP":"Landkreis","GEMEINDE_NAME":"Aach","GEMEINDE_LAT":"4978960","GEMEINDE_LON":"659052","ID_0":"2","ORT_NAME":"Aach","ORT_LAT":"4978972","ORT_LON":"659055","PLZ":"54298"}}]';
$newData=json_decode($data,true);
echo '<pre>';
print_r($newData);
echo '</br>';

    echo 'the field you are looking for is : '.$newData[0]['result']['BUNDESLAND_NAME'];

And the output is :

Array
(
    [0] => Array
        (
            [status] => success
            [result] => Array
                (
                    [BUNDESLAND_NAME] => Rheinland-Pfalz
                    [KREIS_TYP] => Landkreis
                    [GEMEINDE_NAME] => Aach
                    [GEMEINDE_LAT] => 4978960
                    [GEMEINDE_LON] => 659052
                    [ID_0] => 2
                    [ORT_NAME] => Aach
                    [ORT_LAT] => 4978972
                    [ORT_LON] => 659055
                    [PLZ] => 54298
                )

        )

)

 the field you are looking for is : Rheinland-Pfalz

So here i provide you how your array looks like and how i access the specific element you wanted. I hope it's clear.