A modified type of preconditioner is constructed with the help of local block factorization of block tridiagonal matrices. Then the existence and the properties are analyzed. For the standard 5-point matrices, which are derived from the 2-D Laplace operator, the actual condition numbers of the preconditioned matrices are computed. The result shows that the condition number is proportioned to the square root of the order of the matrix. What's more, the longer the step of the local factorization, the smaller the coefficient is. Then efficient implementations of the preconditioners are focused on and three of them provided. Finally lots of experiments are performed for the constructed preconditioners and the well-known effective ones on the personal computer with main frequency of 550MHz and memory of 256M. The matrices in these experiments include the standard five point ones, and the ones derived from a 2-D elliptic operator with discontinuous coefficients. The results also show that the preconditioners are more efficient than the other tested ones.