The invention discloses a real-time working condition diagnostic method for a belt type oil pumping unit. The real-time working condition diagnostic method comprises the following steps: 1, analyzing and calculating a suspension point movement model of the belt type oil pumping unit so as to obtain a relationship between the speed and the displacement of a suspension point, and establishing a power and suspension point load conversion model; 2, according to the power and suspension point load conversion model, converting a typical indicating diagram to a motor power diagram curvature with displacement as an X coordinate and motor power as a Y-coordinate, and establishing a motor power diagram working condition diagnostic model; and 3, collecting the real-time motor power diagram of the belt type oil pumping unit, comparing the real-time motor power diagram with the motor power diagram working condition diagnostic model, and realizing real-time working condition diagnosis. The method enhances the real-time monitoring and working condition diagnosis of the belt type oil pumping unit and increases the production efficiency of the belt type oil pumping unit. The method can extract typical characteristic values from the motor power diagram working condition diagnostic model, facilitates the comparison and working condition judgment of the real-time motor power diagram, easily realizes automatic diagnosis, is high in accuracy and high in speed, and helps enhancing the intelligent management of an oil field.