Mechanical evolution of soymilk coagulation was investigated using a novel fiber optic sensor in order to solve the problem of instability in Chinese traditional tofu quality. The sensor signal was measured, and studied the effects of temperature, soymilk concentration, and calcium chloride solution concentrations on tofu making parameters. The scattering light ratio followed a sigmoid increase during soymilk coagulation. Tofu firmness, tofu moisture content, and tofu yield were predicted from the time to the maximum slope of the first derivative of scattering light ratio. The proposed mathematical model shows potential for on-line monitoring of soymilk coagulation.