var jsonData;
    $.ajax({ 
             type: "Get",  
             url: "/jsn.html", 
             dataType: "text",  
             global: false,  
             async: false,   
             success: function (strReult) { 
                jsonData=eval("("+strReult+")");  
             }, 
             error: function () { 
                alert("Ajax请求数据失败!"); 
             } 
    }); 
              
       for(var i=0;i<jsonData.city.data.length;i++){ 
        
        alert(jsonData.city.data.name);
        
        
       } 

{"city":{
        "data":[
                  {"a":116.420605,"b":40.080577,"name":"碧水宾馆",address:"天通北苑一区甲6"},
                  {"a":116.42048,"b":40.056286,"name":"悦嘉酒店",address:"北京市朝阳区汤立路218号明天生活馆B座"},
                  {"a":116.668862,"b":40.120904,"name":"北京顺则兴商店",address:"北京市顺义区xx"}
                  ]
        }
        }

//alert(jsonData.city.data.name);//少了索引了
  alert(jsonData.city.data[i].name);