Life re-insurers are exposed to mortality catastrophe risk. Mortality CAT bonds are a tool that can mitigate this risk. However, a key disadvantage of this tool is the existence of population basis risk, which occurs whenever there are differences between reference and insured populations. In this thesis, we propose a method to measure population basis risk of mortality CAT bonds. We consider a fictitious mortality CAT bond based on the mortality rates of two regional populations. We first obtain mortality change indexes by calibrating the MBMM model on these two regional populations. Then we use copula-based semi-parametric models to simulate the serial dependence and interdependence structure simultaneously between two regional mortality change indexes. Finally, we analyze the hedge effectiveness of the bond, from which we are able to quantify the population basis risk. We find that population basis risk decreases under certain circumstances.