哪些因素可以导致NOESY 中的cross peaks 变宽呢

Actually it should be arised by the 1D peak broadening.
I checked some materials, and got three probabilities.

From Wuthrich's book:
if the atom is kinetically stable,it should be related to intrisic T2 or pure T2;
if the atom is active, there exists exchange processes,which cause line broadening;
experimental artifacts, say the inhomogeneity of the static field Bo, which can be improved by shimming.

In protein NMR study, CPMG is usually employed to investigate the dynamics.
I recommend two articles:
Science,V.312,14 April,2006,Pp224-227;
JBNMR, V.31,No.4,April,2005,Pp337-342.
They are inspiring.

(Sorry, there is no chinese system in our lab computer!)