  We observe the magnetic field morphology towards a nearby star-forming
filamentary cloud, G202.3+2.5, by the JCMT/POL-2 850 {\mu}m thermal dust
polarization observation with an angular resolution of 14.4" (~0.053 pc). The
average magnetic field orientation is found to be perpendicular to the
filaments while showing different behaviors in the four subregions, suggesting
various effects from filaments' collision in these subregions. With the
kinematics obtained by N2H+ observation by IRAM, we estimate the plane-of-sky
(POS) magnetic field strength by two methods, the classical
Davis-Chandrasekhar-Fermi (DCF) method and the angular dispersion function
(ADF) method, B_{pos,dcf} and B_{pos,adf} are ~90 {\mu}G and ~53 {\mu}G. We
study the relative importance between the gravity (G), magnetic field (B) and
turbulence (T) in the four subregions, find G > T > B, G >= T > B, G ~ T > B
and T > G > B in the north tail, west trunk, south root and east wing,
respectively. In addition, we investigate the projection effect on the DCF and
ADF methods based on a similar simulation case and find the 3D magnetic field
strength may be underestimated by a factor of ~3 if applying the widely-used
statistical B_{pos}-to-B_{3D} factor when using DCF or ADF method, which may
further underestimate/overestimate related parameters.
