The Laplacian characteristic polynomials of the structures of graphs combined with corresponding Laplace matrices were studied. The limit points of the Laplacian spectral radii were provided according to the properties of Laplacian characteristic polynomials. For three types of graphs, the existence of limit points of the Laplacian spectral radii was proved and it was determined when n→∞, the Laplacian spectral radius of a graph is the largest root of certain equation by using some Laplacian characteristic polynomials of the graphs after coalescent operations and considering the upper and lower bounds of Laplacian spectral radii of the graphs.