The method includes scanning a sample in at least one first scan line using a first charged particle beam probe; scanning the sample in at least one second scan line using a second charged particle beam probe, and scanning the sample in at least one third scan line using the first charged particle beam probe. The first or second charged particle beam probe is defocused by a control module of the imaging system through adjusting a condenser lens module, an objective lens module, a sample stage of the imaging system, or their combination. An image of the sample is selectively formed from the first, second and third scan lines. The first and the second charged particle beams induce a first charging condition and a second charging condition on the sample surface respectively. The second charging condition can enhance, mitigate, eliminate, reverse or have no effect on the first charging condition.