我得到了解决方案,
NSString* refresh =your refresh token;
NSString* clientId =[NSString stringWithFormat:@"%@",[BoxSDK sharedSDK].OAuth2Session.clientID];
NSString* clientSecret =[NSString stringWithFormat:@"%@", [BoxSDK sharedSDK].OAuth2Session.clientSecret];
ASIFormDataRequest *postParams = [ASIFormDataRequest requestWithURL:[NSURL URLWithString:@"https://www.box.com/api/oauth2/token?"]];
[postParams setRequestMethod:@"POST"];
[postParams setPostValue:@"refresh_token" forKey:@"grant_type"];
[postParams setPostValue:refresh forKey:@"refresh_token"];
[postParams setPostValue:clientId forKey:@"client_id"];
[postParams setPostValue:clientSecret forKey:@"client_secret"];
[postParams startAsynchronous];
postParams.delegate = self ;
postParams.userInfo = [NSDictionary dictionaryWithObject:@"accessToken" forKey:@"id"];
NSLog(@"Url is ---> %@",postParams.url);