  The spin-1 quantum Ising systems with three-spin interactions on
two-dimensional triangular lattices are studied by mean-field method. The
thermal variations of order parameters and phase diagrams are investigated in
detail. The stable, metastable and unstable branches of the order parameters
are obtained. According to the stable conditions at critical point, we find
that the systems exhibit tricritical points. With crystal field and biquadratic
interactions, the system has rich phase diagrams with single reentrant or
double reentrant phase transitions for appropriate ranges of the both
parameters.
