With the increasinglydemanding for navigation and positioning about BD second generation satellite system,many users’applicationsare in the city,jungle,interior and complex environments,such as the battlefield of human disturbance.Therefore the requirement for receiver becomes more and more high,in order to meet the demand of the application of complex environment,high sensitive receiver has become a hot topic in the current navigation of receiver in the field of technology.In this paper we propose the algorithm of weak signal,the main content include studying on fine acquisition、coherent integral for long time,EKF tracking and a synchronous and related techniques so on.