Abstract: Entangled coherent states are a type of important continuous-variable entangled states in the processing of quantum information.However,it is complicated to calculate their entanglement due to the non-orthogonality of basis vectors in the representation of coherent state.We propose a construction method of a set of complete and orthogonal bases for two-mode entangled coherent states,and simplify the calculation of their entanglement.And also,the entanglement of several typical entangled states is calculated and discussed.

Key words: entanglement measure, orthogonal basis vector, entangled coherent state