The invention provides an inner sliding block mechanism of a special-shaped cam of an injection mold. According to the inner sliding block mechanism, an inner sliding block and a push rod are slidablyarranged in a rear mold plate; the inner sliding block comprises a perpendicular part and a transverse part positioned in the lower segment of the perpendicular part; the upper segment of the perpendicular part extends into a rear mold core; the push rod perpendicularly penetrates through the center of the transverse part and extends into the rear mold core; a spring connected with the transversepart of the inner sliding block sleeves the push rod; a return press block being in contact with the top end of the push rod is arranged in a front mold plate; a base is mounted below the positon, corresponding to the inner sliding block, between two mold feet; the special-shaped cam and an abrasion-resistant block are sequentially arranged in a groove in the inner upper end of the base; a positioning pin capable of driving the special-shaped cam to rotate is arranged at the center of the special-shaped cam; two ends of the positioning pin are embedded in arc-shaped sliding grooves; the arc-shaped sliding grooves are formed in the base and inclined towards the upper right; the left bump of the special-shaped cam is in contact with the bottom surface of the perpendicular part; and the right bump of the special-shaped cam is in contact with the bottom end of the push rod. The inner sliding block mechanism provided by the invention has the advantages that the structure is simple; the quantity of parts is small; the mold size is small; and the manufacturing cost as well as the assembly and maintenance cost are low.