A control method for controlling the composite motion of a boom of concrete distributing device, comprising the following steps: calculating a flow of a boom pump when an instruction is sent from an operating handle; and calculating theoretical demanded flows for each of the actuating mechanisms of the boom and theoretical control signals for each of electrical proportional control valves corresponding to the actuating mechanisms, according to the instruction sent from the operating handle; comparing the sum of the theoretical demanded flows for the actuating mechanisms with the flow of the boom pump; and providing the theoretical control signals to the electrical proportional control valves when the flow of the boom pump is greater than or equal to the sum of the theoretical demanded flows of the actuating mechanisms; otherwise providing actual control signals smaller than the theoretical control signals to the electrical proportional control valves, thereby reducing the movement speeds of the actuating mechanism proportionally; wherein the theoretical control signals for the electrical proportional control valves are i 1, i 2...i n, and the actual control signals are i 1 ', i 2 '... i n ', characterized in that when the sum of the theoretical demanded flows A of the actuating mechanisms is greater than the flow actually provided by the boom pump B, the actual control signals for the electrical proportional control valves are i n '= k*i n + (1 - k) i n 0, where, the coefficient k=B/A, where i n ' and i n are current or voltage signals and i n0 is the minimum current or voltage control signal for the electrical proportional control valves. calculating a flow of a boom pump when an instruction is sent from an operating handle; and calculating theoretical demanded flows for each of the actuating mechanisms of the boom and theoretical control signals for each of electrical proportional control valves corresponding to the actuating mechanisms, according to the instruction sent from the operating handle; comparing the sum of the theoretical demanded flows for the actuating mechanisms with the flow of the boom pump; and providing the theoretical control signals to the electrical proportional control valves when the flow of the boom pump is greater than or equal to the sum of the theoretical demanded flows of the actuating mechanisms; otherwise providing actual control signals smaller than the theoretical control signals to the electrical proportional control valves, thereby reducing the movement speeds of the actuating mechanism proportionally; wherein the theoretical control signals for the electrical proportional control valves are i 1, i 2...i n, and the actual control signals are i 1 ', i 2 '... i n ', characterized in that when the sum of the theoretical demanded flows A of the actuating mechanisms is greater than the flow actually provided by the boom pump B, the actual control signals for the electrical proportional control valves are i n '= k*i n + (1 - k) i n 0, where, the coefficient k=B/A, where i n ' and i n are current or voltage signals and i n0 is the minimum current or voltage control signal for the electrical proportional control valves.