The invention relates to a method for calculating a grounding force of a pitching mechanism of a bucket wheel material stacking and taking machine and an online monitoring system utilizing the method. The method comprises the following steps: establishing a mechanism model, simplifying the mechanism model, carrying out force analysis, detecting a pitching angle and a driving force, calculating an included angle between a weight and a cantilever and the grounding forces at different pitching angles, and establishing a grounding force online calculation model. The online monitoring system comprises a sensing detection subsystem, a data processing subsystem, an error compensation subsystem, a grounding force calculation subsystem, a working condition judgment subsystem and a fault auto-diagnosis subsystem. According to the method, the grounding force of the pitching mechanism of a bucket wheel machine can be calculated on line when the bucket wheel machine normal works, the operation state of the bucket wheel machine can be monitored on line, and alarm is given out when the grounding force is abnormal, so that the safe operation capability of the bucket wheel machine is improved, the machine halt of the bucket wheel machine caused by the grounding force is reduced, meanwhile, the grounding force measurement cost is saved, and the operation cost of an enterprise is lowered.