The invention discloses a tool for detecting surface drying time by constant force and its working method. The tool comprises a metal bracket, a metal link rod and a testing end; the metal link rod isconnected with the metal bracket through a link rod fixing shaft, and the metal link rod forms a lever structure by taking the link rod fixing shaft as a supporting point; the lower end of the metallink rod is connected with the testing end, and the testing end comprises a testing cap and a supporting base; the supporting base is placed at the lower part of the testing cap, and free from directcontact with the testing cap under the initial state of the tool for detecting the surface drying time by constant force; the supporting base is used for placing the testing sample. The tool for detecting surface drying time by constant force has the advantages of effectively testing the surface drying time of the RTV coating, reducing the testing workload and improving the testing efficiency.