An oil filling opening insert mounting mechanism of an oil tank mould comprises a support fixedly arranged in an oil tank mould cavity, and a fixed plate (2) and a first air cylinder (3) are arranged on the support (1); a platform (4) is in sliding connection to the fixed plate (2), and a through hole (5) allowing the fixed plate (2) to penetrate is formed in the platform (4); the end face, close to the first air cylinder (3), of the platform (4) is connected with a piston rod of the first air cylinder (3), and a second air cylinder (7) and a sliding block (8) are arranged on the end face, away from the first air cylinder (3), of the platform (4); the sliding block (8) is in sliding connection to the platform (4), and is connected with a piston rod of the second air cylinder (7); and an oil filling opening insert clamping component is arranged on the sliding block (8). Compared with the prior art, the oil filling opening insert mounting mechanism has the advantages that the product precision and tightness are good, the yield can be greatly improved, the product production cost can be greatly reduced, and the use stability of a product can be improved.