Abstract: A reasonable and precise formation damage evaluation is of great significance in guiding the development of oil and
gas reservoir. The conventional method for formation damage evaluation mainly depends on skin factor and the McKinley type
curves match，by which the permeability of the damaged zone can be calculated. However，because of the solution ambiguity
of the McKinley match，this method may result in great deviation，which further influences the accuracy of decomposition of
skin factor. A new model of modified McKinley well testing analysis method is established，and then its solution is got by
the Laplace transformation. Moreover，the new theoretical type curves（the modified McKinley type curves）are drawn up by
programming. Eventually a new analysis method of matching that can precisely calculate the permeability of damaged zone
is obtained. Hawkins formula is used to calculate true shin factor and the damaged radius，and on the basis of we evaluate
formation damage of well testing permeability of the damaged zone，true shin factor and the damaged radius. Finally the cases
of real oil wells are illustrated and the results accord with the fact，which can be references to formation improvements and
measures taking.

Key words: permeability of the damaged zone, true skin factor, the damaged radius, formation damage evaluation, well testing