  A systemical analysis of the initial fluctuation effect on the collective
flows for Au+Au at 1$A$ GeV has been presented in the framework of
Isospin-dependent Quantum Molecular Dynamics model (IQMD), and a special focus
on the initial fluctuation effect on the squeeze-out is emphasized. The flows
calculated by the participant plane reconstructedby the initial geometry in
coordinate space are compared with those calculated by both the ideal reaction
plane and event plane methods. It is found that initial fluctuation weakens
squeeze-out effect, and somediscrepancies between the flows extracted by the
above different plane methods appearwhich indicate that the flows are affected
by the evolution of dynamics. In addition, we found that the squeeze-out flow
is also proportional to initial eccentricity. Our calculations also
qualitatively give the similar trend for the excitation function of the
elliptic flow of the FOPI experimental data. Finally we address the nucleon
number scaling of the flows for light particles. Even though initial
fluctuation decreases the ratio of $v_4/v_2^2$ as well as $v_3/(v_1v_2$) a lot,
all fragments to mass number 4 keep the same curve and shows independent of
transverse momentum.
