Abstract: A fast constellation selection method was proposed for the low-cost, GPS/SINS (global positioning system/strap-down inertial navigation system) tightly coupled navigation system. To avoid much time-consuming numerical iteration when GPS satellites in the condition of missing lock or constellation geometric distribution changed, geometric dilution of precision(GDOP) estimation carried out taking full advantage of SINS's information. Besides, according to this method, a way of on-line correction to variance covariance matrix of measurement noise has been designed for the tightly coupled integrated navigation system. The result of experiments shows that the proposed method really reduces the number of time-consuming in the procedure of constellation selections, increases accuracy in integrated navigation system, and reduces equipment costs accordingly.