I found an ugly solution to this problem, just drag image from Assets.xcassets to project。 just use UIImage(named: "btn_trend_release") works well。 but app size may increase

as LimingWan said trans png to 8 bit is fine。 simple use python fix install PIL pip install pillow from PIL import Image def deal_png_at_location(root): for root, dirs, files in os.walk(root): for file in files: if file.endswith(".png"): img_path = os.path.join(root, file) img = Image.open(img_path) # whether this file is an 8-bit png, skip it if not if img.mode != "P": continue img = img.convert("RGBA") img.save(img_path) deal_png_at_location("./Assets.xcassets")