The invention provides a building floor thickness detector, the structure of which includes a handle, a power supply casing, a blockade strip, a receiving plate, a thickness measurement outreach device, a display, and a control button, the handle is fixedly connected with the power supply casing, and the blockade strip is embedded Installed on the side of the power supply casing, the handle is fixedly connected with the display, the receiving plate is installed on the right side of the display, the control button is embedded in the hand, and the receiving plate is fitted with the thickness measurement and extension device. During the working process of the present invention, The thickness measuring outreach device can be separated first, and the four extension mechanisms can be stretched toward the outside, and the middle sub-panel for receiving the connection line is fixed in the main sub-panel and used as the central measurement point at one end of the wallboard Expanding, the floor thickness gauge is used for detection at the other end, and only one person can accurately complete the thickness detection of the two opposite test surfaces of the floor through the transmitting probe and the receiving probe, and it is not easy to have deviations.