Some basic problems of Lyapunov Characteristic Exponents (LCE) are discusse
d, including the computational method and the fact that the Lyapunov expone
nt of any limit set other than an equilibrium point must be zero, namely on
e of the Lyapunov exponents should vanishes. The conclusion is deduced that
the dimension of a hyper-chaotic attractor must be great than 3. The LCEs
of several important models are studied, more reasonable results are yielde
d. An efficient method for calculating the conditional LCEs is suggested. B
y studying the conditional LCEs of the hyper-chaotic system, we conclude th
at it cannot be synchronized with only one driving variable. The infection
of random initial values in Wolf's program of LCEs computation is pointed o
ut.