Heavy oil suffers poor fluidity and high viscidity, which poses the main challenge in its exploitation. The reduction of its viscosity is a key to solve this problem. A chemical thermal and catalysis system which is suitable for the heavy oil reservoir is developed. Based on the orthogonal experiment of NaNO₂/NH₄Cl, the order and the contribution rate of every experiment factor on the target index are determined by means of the range analysis and ANOVA analysis, respectively. By testing the oil before and after the reaction by three catalytic systems, a suitable type of catalytic systems is selected, and the oil after the reaction by the selected catalytic system is analyzed by the gas chromatography. It is found that the influences of different factors on the temperature peak are in the following order: the concentration > the value > the initial reaction temperature. The NaNO₂/NH₄Cl sample with concentration of 4mol/L can raise the sample temperature by 150℃ at the initial reaction temperature of 60℃; and the Oleic acid nickel is an effective heavy oil viscosity reducer, with a viscosity reduction rate of 80.3%, a significant decrease of the contents of asphaltenes and pectin and an increase of the contents of asphaltenes and saturated hydrocarbon. The laboratory physical simulations show that the smaller the size of the slug, the better is the result. When the size of the slug is 0.1 PV, the oil displacement efficiency can increase 15.6%.