The invention discloses a self-supported all-welded plate type heat exchanger, which is formed by welding adjacent heat-exchanging plate main bodies and is characterized in that protruding and sinking cone frustums are uniformly distributed on rectangular heat-exchanging plates at interval, opposite edgefolds are arranged at two parallel edge sides of each heat-exchanging plate only, and the height of each edgefold is the sum of the protruding height and the sinking depth of each cone frustum; and half of the edge-folded heat-exchanging plates and the other half of edge-folded heat-exchanging plates are arranged in a manner of equidirectionally arranging adjacent edgefolds by 90 degrees, the protruding cone frustums and the sinking cone frustums of every two plates are opposite, edge-folded end faces and the non-folded edges of the heat-exchanging plates are welded mutually by an angle of 90 degrees, thus, a 90-degree rectangular-block heat exchanger with mutually crossing channels are formed, the edges of four opposite faces of the heat exchanger are respectively welded in an edge extension manner on a same plane to form a border which is connected or welded with bolts of a fan cover, and an air leading-in port and an air leading-out hole of same media are spaced by 180 degrees. The self-supported all-welded plate type heat exchanger has the advantage that the problem on recovering waste heat under running micro-resistance during gas-gas heat exchanging of low-pressure or micro-pressure high-temperature tail gas, smoke and the like is solved.