[en] The effect of deflected channel on particle motion is equivalent to modulation with a weak-potential having a periodic same as the deflected channel has. The motion equation of a particle has been reduced to the nonlinear differential equation with a weak-periodic modulation by using sine-squared potential. The dechanneling fraction has been derived for a strained superlattice. The main-resonance and sub-resonance have been investigated by using multi-scale method, a global bifurcation and the critical conditions with Smale horse shoe have been analysed by using Melnikov method