Abstract: There is no uniform standard for determining the drainage effective radius of CO₂ phase transition fracturing in view of the fact, we analyze the traditional measurement for drainage effective radius, clarify definition of drainage radius. The time-source method is established based on SF₆ tracer method and test data, and it was tested in coal mine. The research shows there is time effect between drainage influence radius and drainage effective radius, and the drainage time is the key factor to distinguish them; the time-source method divides the drainage time into drainage effective time and drainage compensation time. The drainage effective radius under a certain time is obtained through SF₆ tracer method and analysis of the field data. It can reflect the drainage situation of boreholes more accurately; the test-in-place experimented at main haulage roadway in No.3 coal seam of Daping Coal Mine. The result shows that the drainage effective radius after CO₂ phase transition fracturing is 12 m when the drainage time is 120 d and drainage effective radius is 16 m when the drainage time is 148 d.