Steam channeling is a serious problem during steam flooding in heavy oil reservoir. In this paper, an improvement measure was introduced to enhance oil recovery by injecting temperature-resistant gel during steam flooding in heavy oil reservoirs. A two-dimensional (2D) visualization physical model was designed to study the characteristics of viscous fingering and steam channeling during steam flooding. After steam channeling, temperature-resistant gel was injected into the 2D model. Then, the macro- and microscopic mechanisms of improving the development effect were analyzed after gel injection during steam flooding. The experimental results showed that steam channeling was easily formed between the injection well and the production well, resulting from a large viscosity difference of oil steam or serious heterogeneity of formation, which led to a lower sweep efficiency. Gel first flowed into channeling paths and occupied large pores between the particles to make injected steam bypass mainstream channels and further improved oil recovery. The results showed that the final sweep efficiency after gel injection can reach 82.69%, which was 35.91% higher than steam flooding. The ultimate oil recovery was 60.45%, which was 15.17% higher than steam flooding.