[Solved]-Plot Highchart multiple series line chart using JSON data-Highcharts

your date in json should be string. this date should be converted to millisecond.

var json = [{
  name: "maintenance",
  data: [
    ['2017-06-26', 1.5],
    ['2017-07-03', 5.2],
    ['2017-07-10', 1.65],
    ['2017-07-17', 2.5],
    ['2017-07-24', 1.5]
  ]
}, {
  name: "others",
  data: [
    ['2017-06-26', 1.5],
    ['2017-07-03', 1.5],
    ['2017-07-10', 1.5],
    ['2017-07-17', 1.25],
    ['2017-07-24', 1.5]
  ]
}, {
  name: "project",
  data: [
    ['2017-06-26', 6.5],
    ['2017-07-03', 6.1],
    ['2017-07-10', 6.7],
    ['2017-07-17', 7],
    ['2017-07-24', 6.5]
  ]
}, {
  name: "training",
  data: [
    ['2017-06-26', 0],
    ['2017-07-03', 0.75],
    ['2017-07-10', 1.9],
    ['2017-07-17', 0.5],
    ['2017-07-24', 1]
  ]
}, {
  name: "day-off",
  data: [
    ['2017-06-26', 0],
    ['2017-07-03', 0],
    ['2017-07-10', 0],
    ['2017-07-17', 0],
    ['2017-07-24', 1]
  ]
}];
//updating jsons date to millisecond
object.keys(json).map(function(key, index) {
  json[key].data.map(function(value, keys, index) {
    json[key].data[keys][0]=new date(value[0]).gettime()
  })
});
//console.log(json)

fiddle demo