Purpose: To clarify the relationship between the pressure generated during impressions (impression pressure) and the presssure beneath the corresponding denture base (functional pressure) and to examine the influence of tray modifications. Materials and Methods: Impression and functional pressures were measured on models with the same appearance but different bone morphologies for comparison. Pressures with modified trays with additional relief and escape holes were also measured for comparison. Results: The correlation between impression pressure and functional pressure was high, and both could be changed by tray modifications. Conclusion: The distribution of impression pressure will be recreated beneath the denture base, and modifications of trays can control the pressure distribution.