The heat transfer enhancement of the longitudinal vortex (LV) is a kind of technology with high efficiency and low thermal resistance. An LV is produced by longitudinal vortex generators (LVGs). Due to their relative long influence distance and simple structure, the LVGs may be used in narrow channels with a flat surface. In this paper, the dimension of a narrow rectangular channel is 600 mm (length) x 40 mm (width) x 3 mm (height), and one LVG is 14 mm (length) x2.2 mm (width) x 1.8 mm (height). The rectangular blocked LVGs are periodically laid out in the heated plate, and the attack angle of LVGs is 44 degrees, the longitudinal pitch between LVGs is 100 mm, and the transverse pitch between LVGs is 4 mm. The test section is visual with three surfaces and heated with one surface by direct current. The working fluid is water. The experimental results show that the boiling heat transfer coefficient on the heated surface is increased by 25.8%, while the pressure drop along the test section is increased by 50.6%. At the same time, the visual experimental data shows that the bubbles' behavior has been intensively affected by LVs, the growth and gathering of bubbles have been depressed, and the thermal boundary layer in the test section has been greatly damaged and reduced; as results, the momentum and energy exchange in the test section have been strengthened. Thus, the heat transfer is obviously enhanced by LVs.