High temperature approximation (HTA) is used to describe the phase behavior of polydisperse Yukawa hard-sphere chain fluid mixture with chain length polydispersity. It is demonstrated that in the frames of the HTA the model belongs to the class of 'truncatable free energy models', i.e. the models with thermodynamical properties defined by the finite number of generalized moments. Using this property we were able to calculate the complete phase diagram (i.e. cloud and shadow curves as well as binodals) and chain length distribution functions of the coexisting phases. (C) 2007 Elsevier B.V. All rights reserved.