Due to the finite size effect (including the finite sample thickness and the indenter tip size), Hertz's solution cannot accurately describe the indentation behaviour of soft matter. In addition, soft matters are typically viscous and are thus loading history dependent. There might be a coupling between the indentation loading history and the finite size effect, and thus the indentation loading curve of soft matters might be too complex to determine the mechanical properties from it. Using finite element modelling, the indentation loading response of soft matters is investigated based on the commonly used viscous models, including the power-law rheology model and the standard linear solid model, as well as the general viscous model that we have proposed. The results show that the finite size effect does not depend upon the loading history, which also suggests that the finite size effect does not depend upon the material model but only relates to the geometric parameters, such as indenter tip size and indentation depth. With this finding, the mechanical properties of soft matter with finite size (e.g. biological cells) can be determined by indentation tests, not only from the frequency domain but also from the time domain (the quasistatic indentation loading curve), which makes the indentation technique a powerful tool to measure the mechanical properties of soft matters with finite size.