The in-plane mechanical behavior of cold-formed thin-walled steel floors were studied by horizontal low cyclic loading test on three full scale floor specimens. The failure features and bearing capacity indicator of floor specimens as well as the failure mode of self-tapping screw connections were investigated. Test results show that the failure mode of floor specimens were shear failure of self-tapping screws connecting the corrugated metal deck and C-shaped end joists. Based on the in-plane failure phenomenon of the floor specimens, experimental research was conducted on shear behavior of two forms of self-tapping screw connection including self-tapping screws connecting C-shaped and U-shaped joists, self-tapping screws connected corrugated metal deck and end C-shaped joists. And the failure mode and shear capacity of single self-tapping screw connection were obtained. The applicability of single self-tapping screw shear capacity calculating methods in Chinese code GB 50018-2002 was analyzed by the test. Performance-based seismic design theory was adopted to study the performance level, performance target and bearing capacity index of self-tapping screw connections in cold-formed thin-walled steel floors, which can provide reference for the seismic design of cold-formed thin-walled steel structural system.