A light-trapping cancer cell stage testing method includes: measuring a first average escape velocity or range of first cancer cells and a second average escape velocity or range of second cancer cells whose stage is known and differ from that of the first cancer cells and whose types are known; utilizing the first average escape velocity and the second average escape velocity to calculate a reference ratio to build a database; selecting stage-unknown cancer cells and measuring an escape velocity of the stage-unknown cancer cells (type-known); utilizing the escape velocity of the stage-unknown cancer cells and an escape velocity of reference-stage cancer cells to calculate a ratio; and determining a stage of the stage-unknown cancer cells with a result comparing the ratio of the escape velocities for the stage-unknown cancer cells with the reference ratios stored in the database.