Simulation software is one of the crucial parts in digital signal processing education. Most of the subject relies on mathematics of digital signals that is absolutely abstract. Simulation software helps to predict and visualize the result. However most of the software available today is focused on the scientific result and usually is large and expensive that makes them hard to be integrated with lecture slides, websites or other course materials. This problem can be solved by a lightweight interactive simulation software that is much more compact but provides more convenient way of simulating fundamental concepts. This work propos es the design of block diagram style nteractive simulation for digital signal processing. The work covers the algorithm and the object-oriented design of the simulation core that can be used as a backend system for any block diagram simulation software. The design can be implemented in any object-oriented programming language and provides high flexibility in applying to a frontend software. Although this work mainly focused on the algorithm idea and object-oriented designs, the prototype software has been written in c sharp programming language as a proof-of-concept with the result that, the prototyping software can work correctly according to the design.