创建一个类来保存数据。
使用http://jsonutils.com/之类的工具，您可以粘贴json并返回

public class Fields
{
    public string key1 { get; set; }
    public string key2 { get; set; }
}

public class RootObject
{
    public long creationTimestamp { get; set; }
    public long lastUpdatedTimestamp { get; set; }
    public long lastStageChangeTimestamp { get; set; }
    public Fields fields { get; set; }
}

Net库允许您将json反串行化到上述类中。

var models = JsonConvert.DesrializeObject<RootObject[]>(json);

var val1 = models[0].key1;
var val2 = models[0].key2;

Please Use Dictionary datatype for fields property
public class RootObject
{
 public long creationTimestamp { get; set; }
 public long lastUpdatedTimestamp { get; set; }
 public long lastStageChangeTimestamp { get; set; }
 public Dictionary<string,string> fields { get; set; }
}