  Within the framework of three generations of leptons the schematical method
for estimating CP asymmetry in neutrino oscillations is considered. We
introduce a unitarity triangle corresponding to \nu_e-\nu_{\mu} oscillation, in
addition, we show that it is convenient for the estimation to define another
new triangle. CP asymmetry is determined by the difference between the shapes
of a unitarity triangle and new triangle. As results, (i) we show that CP
asymmetry becomes maximal if the shapes of these two triangles are the same.
(ii) We can easily estimate L/E which leads almost 100% asymmetry using this.
(iii) In \nu_e-\nu_{\mu} oscillation with \sin^2 2\theta_{13} \simeq 0.04, we
obtain about 90% asymmetry for LMA MSW scenario and 3% asymmetry for SMA MSW
scenario within long baseline neutrino expriments to be realized in near
future.
