Tapered Double Cantilever Beam Compression (TDCBC) test is proposed as a stress intensity factor K decreasing type testing method. In this test, Tapered Double Cantilever Beam (TDCB) specimen is compressed in the direction of the crack growth, and K -value decreases with increase in the crack length under constant load. The increase of the specimen width in the crack growth direction is effective for obtaining K -value decreasing tendency. The compression load is effective for the crack path directional stability. It is recommended that cracked side of two specimens be placed facing each other and compression load is transmitted through a pair of rollers between the specimens. This method is effective in minimizing the constraint in the crack opening displacement. The rollers have to be placed near the edges of the cracked side of the specimen in order to obtain positive K -value. K -value was analyzed numerically and the effects of the specimen geometry and the loading position on K -value were examined. Approximate polynomials for K -value calculation of three kinds of the specimen shape are given. TDCBC static fracture test of PMMA was conducted and fracture characteristics were investigated. It was confirmed that brittle crack grows straightly and stably in the K -value decreasing zone and that K-value of the stably growing crack is almost constant.