  We have developed multi-dimensional constrained covariant density functional
theories (MDC-CDFT) for finite nuclei in which the shape degrees of freedom
\beta_{\lambda\mu} with even \mu, e.g., \beta_{20}, \beta_{22}, \beta_{30},
\beta_{32}, \beta_{40}, etc., can be described simultaneously. The functional
can be one of the following four forms: the meson exchange or point-coupling
nucleon interactions combined with the non-linear or density-dependent
couplings. For the pp channel, either the BCS approach or the Bogoliubov
transformation is implemented. The MDC-CDFTs with the BCS approach for the
pairing (in the following labelled as MDC-RMF models with RMF standing for
"relativistic mean field") have been applied to investigate multi-dimensional
potential energy surfaces and the non-axial octupole $Y_{32}$-correlations in
N=150 isotones. In this contribution we present briefly the formalism of
MDC-RMF models and some results from these models. The potential energy
surfaces with and without triaxial deformations are compared and it is found
that the triaxiality plays an important role upon the second fission barriers
of actinide nuclei. In the study of Y_{32}-correlations in N=150 isotones, it
is found that, for 248Cf and 250Fm, \beta_{32} > 0.03 and the energy is lowered
by the \beta_{32} distortion by more than 300 keV; while for 246Cm and 252No,
the pocket with respect to \beta_{32} is quite shallow.
