Existing literatures on mixed oligopoly markets usually focus on competition relationship among different types of firms.But reality shows cooperation among firms besides the competition relationship.Using a location model, we allow public firm competing with foreign firm, and at the mean time cooperating with it through subcontracting.We find that variation in costs or tariffs has no effect on either firm s position.Tariff on input can raise social welfare and government will charge an input tariffto the extent of costs difference.Tariff on final good has no effect on welfare but will raise prices.Compared to no tariff at all, tariff on inputs alone raises retail prices, but tariffs on both inputs and final goods may reduce prices.Consumer surplus is higher when retail prices are lower.We also find that comparing to competing with domestic private firm, when public firm competing with foreign firm, social welfare is lower, but consumer welfare is higher.