The file size depends on the image you insert. Plugins works directly with the content of your clipboard and saves it in PNG format. If you have copied big image - you will have a big file. (plugin author)

I copied an JPG file just about 300KB, after pasting, the file size is more than 2MB

If you already have a file saved as a JPG, it would be reasonable to upload it as a file, but not the clipboard content. When you save the file to JPG you lose some quality, depending on the JPEG-compression settings. And if you open it, you basically "unpack" it. If you then copy it to clipboard - you will copy it as a new image with all compression artifacts. Resaving it to JPEG again will add more artifacts. I prefere to save the original quality of the images, that's why plugins saves to PNG - to avoid loss of quality. Basically, if you copy your JPG-image to the clipboard, paste it to any image editor and save it to PNG - your filesize will always be bigger than original JPG. I would recommend you two options: 1) If you already have the JPG files - upload them directly with normal file uploader. 2) If you need to use a clipboard but you want to keep the filesize small - use any PNG-to-JPEG converter plugin on bubble. Simply add two more steps in the workflow - convert to JPG and remove uploaded PNG file. (plugin author)

Thank you, Base on your advice, i can resolve my problem