  In this paper, we study the Cabibbo favored three body non-leptonic D^+
\rightarrow K^- \pi^+ \pi^+ decay. We show that the corresponding direct CP
asymmetry is so tiny in the framework of the Standard Model and is out of the
experimental range. Motivated by this result we extend the study of the CP
asymmetry to include a toy model with CP violating weak phase equals 20 degrees
in a_2, a model with extra gauge bosons within Left-Right Grand Unification
models and a model with charged Higgs boson. We show that the toy model can
strongly improve the SM prediction of the CP asymmetry to be about 30%. The
largest CP asymmetry can be achieved in the non-manifest Left-Right models
where a CP asymmetry up to 25% can be reached. For the two Higgs doublets
models the CP asymmetry is of order 10^{-3}.
