The invention relates to a horizontal drilling test device for a rotary steerable tool. The horizontal drilling test device for the rotary steerable tool comprises a steerable device. An integrated lifting platform is movably installed on the steerable device. The integrated lifting platform is supported by a lifting hydraulic cylinder which is arranged below the integrated lifting platform. Makeup and breakout nippers are installed at the front end of the integrated lifting platform. A rotary drilling device is movably installed in the approximately central position of the integrated lifting platform. The rotary drilling device is connected with a drilling pressure hydraulic cylinder through a force sensor. A torque and rotating speed sensor is installed on an output shaft of the hydraulic motor of the rotary drilling device. When the horizontal drilling test device provided by the invention is matched with other test systems, torque and drilling pressure of horizontal drilling can be provided, and the drilling torque and the drilling pressure can be accurately measured and controlled; and since a complete set of makeup and breakout nippers is provided and can be successively connected with a short drilling rod, the continuous drilling test of the rotary steerable tool in a concrete target block at the front of the rotary steerable tool is realized. Moreover, the demands on conducting multi-position drilling tests in the concrete target block at the front of the rotary steerable tool can be met by changing the position of the horizontal drilling test device.