We apply the statefinder diagnostic to the modified polytropic Cardassian universe in this work. We find that the statefinder diagnostic is quite effective to distinguish Cardassian models from a series of other cosmological models. The s-r plane is used to classify the modified polytropic Cardassian models into six cases. The evolutionary trajectories in the s-r plane for the cases with different and reveal different evolutionary properties of the universe. In addition, we combine the observational H(z) data, the cosmic microwave background data and the baryonic acoustic oscillation data to make a joint analysis. We find that Case 2 can be excluded at the 68.3% confidence level and any case is consistent with the observations at the 95.4% confidence level.