  We have developed an efficient Monte Carlo algorithm, which accelerates slow
Monte Carlo dynamics in quasi-one-dimensional Ising spin systems. The loop
algorithm of the quantum Monte Carlo method is applied to the classical spin
models with highly anisotropic exchange interactions. Both correlation time and
real CPU time are reduced drastically. The algorithm is demonstrated in the
layered triangular-lattice antiferromagnetic Ising model. We have obtained the
relation between the transition temperature and the exchange interaction
parameters, which modifies the result of the chain-mean-field theory.
