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In order to overcome the problem that it is difficult to accurately define the downsampling operation for a generalized graph signal in graph filter banks, this paper focuses on the design algorithm of nonsubsampled graph filter banks. Firstly, the spline filters are taken as the analysis filter banks. Then, two different methods are proposed to construct the synthesis filter banks. In the first algorithm, the synthesis filter banks can be constructed with the perfect reconstruction conditions in vertex domain. By taking into account the frequency of the subband filters in the second algorithm, the synthesis filter banks are designed by solving a constrained optimization problem involving the spectrum characteristics of the filters. The design methods can lead to two channel nonsubsampled graph filter banks with perfect reconstruction. Finally, taking the two channel nonsubsampled graph filter banks as a basic building block, multichannel nonsubsampled graph filter banks are constructed，which can realize multiresolution analysis of graph signal through cascading. Simulation results show that the designed nonsubsampled graph filter banks have perfect reconstruction property. Furthermore, the designed multichannel nonsubsampled graph filter banks have better denoising performance than the existing graph filter banks.