Abstract: Instead of traditional Euler angles, rotation vectors were adopted to improve the speed in initial alignment of strapdown inertial navigation system(SINS). In many situations, the system model had an unknown bias and stochastic information, the H∞ filter was applied to improve the convergence of filter. The field test of SINS indicated that the heading was estimated much faster when the rotation vectors-based method was used than which the traditional Euler angle-based alignment method was used.