Abstract: Currently, manual measurement methods such as rotational viscosimeters are mainly used on drilling sites, with long measurement cycles and human interference factors. The existing online measurement devices such as tubular viscometers are affected by factors such as fluid pulsation of the diaphragm pump for extracting drilling fluid, motor vibration, and pressure difference measurement bias error, resulting in poor measurement accuracy and stability. An online calibration method for rheological parameters of drilling fluid based on empirical mode decomposition and maximum likelihood estimation was proposed on the basis of the tubular viscometer of double-tube pressure difference to address the above issues. Firstly, an empirical mode decomposition model was established using measurement data from the pressure difference sensor to extract interference signals caused by diaphragm pump pulsation, motor vibration, and measurement errors, thereby achieving accurate identification of constant current pressure difference signals. Then, a rheological parameter calculation model for the tubular viscometer was established, and the shear stress-shear rate curve of the double tubes was used to establish a calibration model for shear stress parameters of drilling fluid based on the maximum likelihood estimation. Finally, the established online monitoring and testing platform for drilling fluid performance was used for experimental verification. The measurement accuracy of apparent viscosity, plastic viscosity, and dynamic shear force obtained by the proposed online calibration method for rheological parameters was significantly better than that of uncalibrated parameters, and the relative errors of measured apparent viscosity, plastic viscosity, and dynamic shear force were all less than 5%, meeting the requirements of on-site drilling testing. The results show that the method is effective and has high precision, which provides a new way for rapid and accurate measurement of rheological parameters of drilling fluid.