The invention discloses a rotary drum device with an automatic door closing function and relates to the field of testing equipment for the viscosity index of bituminous coal. The rotary drum device comprises a front bearing frame, a rear bearing frame, a driving wheel, a driven wheel, a translational nut, a lead screw, a rotary drum, a low-resistance piston, a fixed door, a movable door, a hopper, a sieve, a waste-material box, a door closing bracket, a door closing shaft, a door closing roller, a closing spring, a main motor and an auxiliary motor, wherein the automatic door opening is realized by common action of a movable baffle plate and the closing spring, automatic closing is realized by common action of the closing roller and the closing spring, and automatic outward pushing is realized by forward movement of the low-resistance piston in the rotary drum. The rotary drum device disclosed by the invention has the advantages that the structure is reasonable, the automatic door opening and closing and automatic material taking are achieved.