Present invention is related to an ultrathin triboelectric nanogenerator having a positive assembly layer and a negative assembly layer electrically connected together. The positive assembly layer comprises a positive layer and a first electrode. The negative assembly layer comprises a negative layer and a second electrode. The said first electrode and the said second electrode are electrically connected with each other. The positive layer could be a foam layer with under 90 μm thickness and less than 60 μm pore size. The present invention firstly provides the ultrathin triboelectric nanogenerator with PU foam as the positive layer which could achieve better electrical performance compared to any conventional triboelectric nanogenerator.