The invention discloses a device and method for testing an effective heating area of a tubular resistance furnace, and the device comprises a temperature measurement mechanism disposed in a tubular furnace and a positioning adjustment mechanism used for installing the temperature measurement mechanism, and one end of the tubular furnace is provided with a temperature control instrument extending into the tubular furnace. The positioning adjusting mechanism comprises a positioning block arranged at the other end of the tubular furnace and a rotating block embedded in the positioning block, a first temperature measuring tube is arranged on the positioning block, a second temperature measuring tube is arranged on the rotating block, and the temperature measuring mechanism comprises multi-section temperature sensors arranged in the first temperature measuring tube and the second temperature measuring tube in a penetrating manner; the method comprises the following steps: 1, installing a temperature measuring mechanism; 2, testing an effective heating area; and 3, determining a uniform temperature area of the tubular furnace. According to the invention, the multi-section temperature sensor is adopted for regional testing, so that the real-time temperature values of different positions in the tubular furnace can be conveniently tested at the same time, the uniformity of the temperature in the tubular furnace and the uniform temperature region can be conveniently determined by technicians, and the testing effect is good.