How to get the customer tax classification form the customer mater to sales orders automatically?

Hi, experts:

In the customer mater, I set  customer tax classification to 1, shown as Fig. 1.

Fig. 1.

But I create  the sales order,  customer tax classification cannot display 1 automatically, shown as Fig. 2.

Fig. 2.

How to get the customer tax classification form the customer mater to sales orders automatically?

Best regards,

Jet.