1. A method for testing a lens under test, applied in a lens testing device, comprising: using a plurality of image sensors of the lens testing device to test the lens under test and provide an image of the lens under test for a first object distance, and obtaining a testing characteristic value of the lens under test for the first object distance according to the image; providing a correction datum comprising relation values of characteristic values between different object distances, and the the step of providing a correction datum comprising obtaining a correction curve for the first object distance; obtaining a correction curve for the second object distance; and forming the correction datum by calculating the relation values between the correction curve for the first object distance and the correction curve for the second object distance; and calculating by a processing unit of the lens testing device a simulated characteristic value for the second object distance according to the testing characteristic value for the first object distance and the correction datum.