The invention discloses a geographical coordinate projection transformation method. The method comprises the steps of extracting the coordinates of a vertex of a transformation area, calculating the coordinates of a homonymy point of the vertex under a target projected coordinate system, setting up a projection transformation linear system of equations, and calculating the coordinates of elements in the projection transformation area under the target projected coordinate system according to the projection transformation linear system of equations. Meridians and latitude lines in a small local area are represented through straight lines respectively, spherical surface calculation is converted to planar calculation, the calculating speed of geographical coordinate projection transformation can be increased, error control can be achieved by controlling the size of the local area, and the requirements of actual application can be met with little cost, wherein the actual application relates to mass data transformation, and the requirements for transformation precision and transformation speed are high.