The application relates to the technical field of nitrite synthesis, and discloses a synthesis method and a synthesis device of alkylnitrite. The synthesis method comprises the following steps: firstly, mixing gaseous nitric oxide and gaseous oxygen to obtain a mixture through a first reaction; and then, mixing the mixture with alkylalcohol to obtain alkylnitrite through a second reaction. The synthesis method greatly shortens the reaction time, increases the yield of alkyl nitrite, does not have a complicated post-treatment process and a large amount of by-product nitric acid, and is beneficial to cost saving and time saving.