If your spouse cannot/does not attend your visa appointment with you, they must write a letter in support of your application. 

The spouse support letter should be clear and concise, stating all of the necessary information for the visa, without lengthy or confusing rambling. It would also be wise to include a list of the evidence and documents you're sending. There is a good example of a spousal visa support letter in the internet archive (past copies of websites which may no longer exist) of Transpondia.