The invention discloses an STI stress effect modeling method and device of an MOS device, and belongs to the technical field of parameter extraction modeling of devices. The method comprises the following steps: introducing the influence of temperature parameters on the STI stress effect of the MOS device, so as to form a function showing that the STI stress effect of the MOS device changes along with the temperature parameters; extracting the model parameter Model1 of the MOS device at normal temperature; on the basis of the Model1, extracting the parameter Model2 that the STI stress affects the properties of the MOS device at normal temperature; and on the basis of the Model2, extracting fitting parameters of the MOS device in the function so as to acquire final model parameters. The device comprises a first module, a second module, a third module and a fourth module. By establishing the function showing that the STI stress effect of the MOS device changes along with the temperature parameters, the influence of the temperature on the STI stress effect of the MOS device can be accurately described, so that the extracted model parameters are more accurate and reliable.