diff --git a/lualib/mongo.lua b/lualib/mongo.lua
index 877982f4..7393ebbd 100644
--- a/lualib/mongo.lua
+++ b/lualib/mongo.lua
@@ -105,12 +105,38 @@ local function mongo_auth(mongoc)
 				mongoc.__sock:changebackup(backup)
 			end
 			if rs_data.ismaster	then
+				if rawget(mongoc, "__pickserver") then
+					rawset(mongoc, "__pickserver", nil)
+				end
 				return
 			else
-				local host,	port = __parse_addr(rs_data.primary)
-				mongoc.host	= host
-				mongoc.port	= port
-				mongoc.__sock:changehost(host, port)
+				if rs_data.primary then
+					local host,	port = __parse_addr(rs_data.primary)
+					mongoc.host	= host
+					mongoc.port	= port
+					mongoc.__sock:changehost(host, port)
+				else
+					skynet.error("WARNING: NO PRIMARY RETURN " .. rs_data.me)
+					-- determine the primary db using hosts
+					local pickserver = {}
+					if rawget(mongoc, "__pickserver") == nil then
+						for _, v in ipairs(rs_data.hosts) do
+							if v ~= rs_data.me then
+								table.insert(pickserver, v)
+							end
+							rawset(mongoc, "__pickserver", pickserver)
+						end
+					end
+					if #mongoc.__pickserver <= 0 then
+						error("CAN NOT DETERMINE THE PRIMARY DB")
+					end
+					skynet.error("INFO: TRY TO CONNECT " .. mongoc.__pickserver[1])
+					local host, port = __parse_addr(mongoc.__pickserver[1])
+					table.remove(mongoc.__pickserver, 1)
+					mongoc.host	= host
+					mongoc.port	= port
+					mongoc.__sock:changehost(host, port)
+				end
 			end
 		end
 	end