<p>Let p be a prime number and F be a finite extension of Q_p. We established an algorithm to compute the semisimplification of the reduction of some irreducible two dimensional crystalline representations with two parameter {h,a_p} when v_p(a_p) is large enough. We improve the known results when p|h. We also extend the algorithm to the two dimensional semistable and non-crystalline representation. We compute the semi-simplification of the reduction when v_p(L) large enough and p=2. These results solve the difficulties with the case p=2. The strategies are based on the study of the Kisin modules over O_F and Breuil modules over S_F. By the theory of Breuil and Theorem of Colmez-Fontaine, these modules are closely related to semistable representations.</p>