On Windows 10:
Download the file from e.g.: https://dl.google.com/android/repository/sys-img/google_apis/x86-27_r09.zip.
Extract the zipped file.
Copy (OR Cut, not recommended) the contents of the extracted folder e.g.: x86.
Find the android-sdk folder. By default, it should be located at C:\Users\[YOUR USER NAME]\AppData\Local\Android\Sdk.
Look for a folder named system-images. Create system-images if it doesn't exist. Depending on the file you downloaded, create subfolders within system-images. E.g.: system-images->android-27->google_apis.
Paste within google_apis.
Restart Android Studio and the system image should be selectable.
Shout if you need any further assistance.
source : https://stackoverflow.com/questions/45686444/android-studio-manually-download-system-image-for-emulator/45686633