how to trigger click event of input file from button click in angular 2?

You can leverage template reference variable as follows:

<input type="file" accept="image/*" #file>
<button (click)="file.click()">Upload file</button>

The corresponding plunkr is here https://plnkr.co/edit/JB4HY0oxEUgXXIht2wAv?p=preview