Cascade control PID was used to adjust the density of the starch production-line. After analyzing and comparing the principle of traditional PID and Smith prediction PID, a mathematical model about cascade control loop of starch production-line was proposed. Then, these two controllers and their outer loop controller were designed and simulated by using tradition PID and Smith prediction PID respectively. The simulation results show that the cascade control system with Smith prediction PID on its outer loop is better than traditional PID. In the end, the implementation of a rapid prototyping control system was presented, which involves the design of DSP algorithms by using Matlab/Simulink blocksets to setup the Simulink module of the starch production-line, automated code generation in the CCS integrated development environment, and downloading of executable code to the Texas Instruments’ TMS320C2812 and TMS320C6713.