DiffSim uses automatic differentiation techniques that automatically calculate gradients by differentiating through the simulator, allowing gradient-based optimization using "backpropagation" to optimize simulation inputs such as force field parameters. Gradient-based optimization requires the computation of reliable gradients. To overcome the issue of instability of gradient computation through the MD solver, we employ the importance reweighting technique as DiffTre 42 to improve the stability of gradients. DiffTre basically creates a proxy function using the thermodynamic perturbation theorem to bypass the differentiation through the entire trajectory for time-independent observables. Given that the structurebased coarse-graining method only addresses static properties as targets, this method is inherently well-suited for such applications.