This paper studies the influence of the ratio of main current & bucking current and the rest potential of the hard focus lateral tool on the logging results, the circuit simplified measurement method of the the ratio of main current & bucking current and the rest potential, simplifies the circuit model of the main current & bucking current measurement of the tool with the help of the forward method, builds the main current test circuit and the bucking current measurement circuit, and gives the theoretical calculation method and the result analysis. The results show that the method can be based on the electricity simplified model, the ratio of main current & bucking current and rest potential test results are given. The test results can correct the errors of the forward model of the tool to a certain extent. The application advantages of this method in the main focus circuit parameter test are analyzed. It can quantize and compare the parameters of the main current measurement in different directions of the array azimuthal laterolog, ensure the consistency of the tool orientation, and provide the data support for the continuous optimization of the main focus circuit.