The present invention relates to a method for obtaining vertical permeability of heavy oil-bearing formation by utilizing isoformation vertical interference test and its testing string for implementing said method. said method includes the following steps: the testing string can utilize packer to retain the upper and lower region of tested object formation and separate upper and lower perforated oil formations; using expansion long rubber barrel packer in the testing string to close middle well-cased perforating fluid flow passage of tested object formation, injecting water into upper portionof oil formation from water-injecting hole on the throttling controller in the described testing string to make impulse excitation, in the lower portion of tested object formation utilizing high-precision electric pressure gauge in the bridge type pressure-measuring meter of testing string to measure the impulse pressure produced by top portion excitation of oil formation, then utilizing receivedpressure parameter to define the vertical permeability of said oil formation.