string str="{\"size\":15,\"query\":{\"match\":{\"data.query.match.promotionInfo.query\":{\"boost\":1.3,\"type\":\"phrase\",\"query\":\"销售1\"}}}}";
var obj = JObject.Parse(str);
var boost = obj["query"]["match"]["data.query.match.promotionInfo.query"]["boost"].ToString();
原文：http://www.cnblogs.com/gaocong/p/5830372.html