Aircraft icing can cause a series of problems such as aerodynamic performance degradation and flight quality degradation of the whole aircraft, which will pose a great threat to flight safety. Modern civil aircraft are generally equipped with ice detectors to deal with the icing problem in flight. The primary ice detection system is a new type of aircraft detection system that can automatically judge whether the aircraft has entered the icing conditions, which can effectively reduce the operating burden of the crew. This paper first introduces the primary ice detection system in detail, including the differences between the primary ice detection system and the traditional advisory ice detection system, the advantages of the primary ice detection system and the main design difficulties of the primary ice detection system. Then the design method of the primary ice detection system based on the magnetostrictive ice detector was described. The main purpose is to identify the ice conditions that can not be detected by the ice detector. By presetting the ice conditions in the controller of the anti-ice system, the anti-ice system can be opened timely under all the ice conditions.