A MATLAB matrix decomposition algorithm for solving initial/boundary value problem of TM wave in two-dimensional photonic crystal is presented.Firstly,the TM wave is expressed as a matrix model by a classic implicit format difference scheme that is absolutely stable.Secondly,the matrix equations about the magnetic field components and the electric field components can be separated by leap-frogging sampling and their solutions can be obtained with matrix left division command in MATLAB.The algorithm is concise in concept,convenient in operation,universal in application and easy in programming.