Cavity pressure measurement is well known but not widely used technique. The goal of this paper is to present the effect of material properties, set up parameters and mould geometry on the cavity pressure curve. Cavity Eye measuring system was installed to Arburg and Engel injection moulding machines. Three kinds of material were used for the tests, and the mould had also different kinds of running system. Apart from the cavity pressure the injection moulding parameters were monitored. More than one sensor was installed to each cavity so the pressure differences could be measured during the filling stage. The filling stage, compression stage and the cooling stage were studied and compared to the injection pressure. It was found that some parameters have significant effect on the pressure peak, the pressure integral and the shape of the curve, but some of them had hardly effect on the internal pressure. The switching over was achieved by screw position and by cavity pressure. According to the results the cavity pressure is more stable if internal switch over is used, but the delay time of the electronic system, so the sampling rate is critical.