The lockrelease is the key factor which influences the northfinding accuracy of the pendulous gyroscope. In order to solve the problem of longtime lockrelease and wide swing range of the pendulous gyroscope, by using a new lockrelease system with uniform motion as a study case and using I2C bus expension of the preexisting control circuit to control lockrelease electrical machine accurately and reasonably, the steady and rapid lockrelease has been realized. The experiment verification show that the new control method is feasible, and both the lockrelease time and swing range have been limited to 25 s and 1°30′ respectively, thus it has feasibility and practical value.