<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> <style type="text/css"> canvas{ background-color: grey; } </style> </head> <body> <canvas id="myCanvas" height="800" width="800"/> </body> <script type="text/javascript"> var c=document.getElementById("myCanvas"); var cxt=c.getContext("2d"); cxt.fillStyle="red"; cxt.arc(100,100,50,0,2*Math.PI,true);//arc花元，100，100里画布距离，50半径， cxt.fill(); </script> </html>