1. A method for obtaining clear images through the rain, snow or fog, wherein, the method comprises the steps of: (A) controlling via a digital signal processor (DSP) processing module a laser pulse generating module to output laser pulse signals with a default pulse width, and shutting the laser pulse generating module down when a first default time period arrives; (B) controlling via the DSP processing module, when the laser pulse generating module is outputting the laser pulse signals, an electronic shutter of an image pick-up device, to open after delaying for a second default time period, and shutting down the electronic shutter when a third default time period arrives, wherein the third default time period is the period of time that the default pulse width of the laser pulse signals lasts; and (C) processing a plurality of video images captured by the image pick-up device through a field-programmable gate array (FPGA) module, so as to make the video images of the output clearer, or increase a capturing distance which obtains clear images; wherein step C comprises the steps of: weighted processing of the video images of a plurality of default frames captured by the image pick-up device, and obtaining an image pixel average value of the video images of the default frames; processing the video images of the default frames by filtering; and extracting a pixel information from each frame of the video images, and combining the video images of the default frames into one video image for output.