In this article, a novel method to calculate the current distribution, which enables the active sidelobe suppression of the magnetic flux density in an synthesized magnetic field focusing (SMF) system, is proposed for the first time. The proposed method calculates the current distribution, which enables further sidelobe suppression and keeping the resolution at the same time, by changing the target magnetic flux density distribution with only one varying parameter. The proposed calculation method is very intuitive and time-efficient compared with the other calculation methods, as it only changes one variable to control the sidelobe with one step of matrix multiplication. With the finite element method simulation, it is verified that the proposed method can suppress the sidelobe with any target Rx point when the SMF system has 14 coils with size of 10 cm x 10 cm, and the synthesis distance is 30 cm. When the field is synthesized at the center, over 90% of the sidelobe is suppressed for maximum case. An figure-of-merit (FoM) is constructed to optimize the system between the resolution increment and the sidelobe suppression, and 79% of the sidelobe is suppressed for the optimized case while keeping the resolution increment ratio below 30%. In addition, it is verified that the method can also be applied to the two-dimensional (2-D) SMF systems. The experimental results were in good agreement with the simulated results when the experimental prototype of the same condition with simulation was utilized, including a case in which the magnetic field is focused at the Rx point other than the center.