  Large-scale high sensitivity laser gyroscopes have important applications for
ground-based and space-based gravitational wave detection. We report on the
development of a 3 m$\times$3 m heterolithic passive resonant gyroscope
(HUST-1) which is installed on the ground of a cave laboratory. We operate the
HUST-1 on different longitudinal cavity modes and the rotation sensitivity
reaches $1.6\times10^{-9}$ rad/s/$\rm \sqrt{Hz}$ beyond 1 Hz. The drift of the
cavity length is one of the major sensitivity limits for our gyroscope in the
low frequency regime. By locking cavity length to an ultra-stable reference
laser, we achieve a fractional cavity length stability of $5.6\times10^{-9}$
m$/\rm \sqrt{Hz}$ at 0.1 mHz, a four orders of magnitude improvement over the
unconstrained cavity in the low frequency regime. We stabilize the cavity
length of a large-scale heterolithic passive resonant gyroscope through active
feedback and realize long-term operation. The rotation sensitivity reaches
$1.7\times10^{-7}$ rad/s/$\sqrt{\rm{Hz}}$ at 0.1 mHz, a three orders of
magnitude improvement, which is no longer limited by the cavity length drift in
this frequency range.
