As the outcome cannot be set by a rule, a workaround could be to:

• Make your task a single outcome task
• Add Decision as a choice field
• Make it mandatory
• Use a rule to set its value and make it read-only conditionally based on the credit limit value
• Back in the workflow, branch on the value of Decision field in the same way you would typically with task outcomes

thank you,

how I can make it based on the company, for example

if the company A the maximum credit limit is 7000

if the company B the maximum credit limit is 10000

Where is this reference information stored? 

You should consider using a data variable and external data in your form to look it up (unless you are dealing with a tiny number of companies and can hard code this logic).

https://help.nintex.com/en-us/nwc/content/Designer/FormsExternalData.htm

e.g. if that information was stored in a SharePoint list or other data source you could use data variables to lookup the credit limit for company A. Then you use the value of that looked up credit limit in your rule.

the value will be stored in sharepoint list, worked, much thanks