  The Cooling-Storage-Ring External-target Experiment (CSR-CEE) is a
spectrometer to study the nature of nuclear matter created in heavy ion
collision at $\sqrt{s_{NN}} = $ 2.1 - 2.4 GeV, aiming to reveal Quantum
Chromodynamics (QCD) phase structure in the high-baryon density region.
Collective flow is regarded as an effective probe for studying the properties
of the medium in high-energy nuclear collisions. One of the main functions of
the Zero-Degree Calorimeter (ZDC), a sub-detector system in CEE, is to
determine the reaction-plane in heavy ion collisions, which is crucial for the
measurements of collective flow and other reaction plane related analysis. In
this paper, we illustrate the procedures of event plane determination from ZDC.
Finally, predictions of the rapidity dependence of directed and elliptic flow
for $p$, $d$, $t$, $^3$He and $^4$He, from 2.1 GeV U+U collisions of IQMD model
calculations, are presented.
