for($i=1;$i<=12;$i++){
    $nextdate = date("Y-m",strtotime("+ $i month"));
    echo '<p>'.$nextdate;
}

// 参数表示好多个月，你也可以修改为指定日期开始
function c($num = 12){
    $temp = array();
    $nowtime = strtotime( date('Y-m', time()) . '-1' );
    while( $num>0 ){
        $num--;
        $nowtime = strtotime( '+1 month', $nowtime );
        $temp[]  = date('Y-m', $nowtime);
    }
    unset( $num, $nowtime );
    return $temp;
}

print_r( c() );