labelMaxWidth: Number

labelMaxWidth defines the maximum width of labels after which they get wrapped or clipped depending on labelWrap’s value.

Default: Automatically calculated based on the length of label.
Example: 4, 20, 100 etc.

var  chart =  new  CanvasJS.Chart("container",
{
 .
 .
 axisY: {
        labelWrap: true     
        labelMaxWidth: 50   //change the width
 },
 .
 .
});
chart.render();