Method of preparing diester-based material

A method of preparing a diester-based material in a continuous preparation process using a reaction part in which a total of n reaction units from a first reaction unit to an nth reaction unit are connected in series, each of the reaction units including a reactor which esterifies a dicarboxylic acid and an alcohol and a lower discharge line, the method comprising:

• esterifying the dicarboxylic acid and the alcohol in the reactor of the first reaction unit to produce a reaction product,
• supplying a lower discharge stream connected to a bottom of the reactor and including the reaction product to at least one reaction unit at a rear end through the lower discharge line;
• and
• supplying a liquid material through a liquid supply line connected to the lower discharge line of the reactor of the first reaction unit thereby controlling a solid fraction and a flow velocity of the lower discharge stream from the reactor,
• wherein a flow rate of the liquid material supplied to the liquid supply line is from 1% to 15% of a flow rate of the lower discharge stream from the reactor of the first reaction unit
• the liquid material includes the alcohol and the lower discharge stream from the reactor of any one or more reaction units including a second reaction unit to the nth reaction unit.