使用AWS CloudFormation为CloudWatch授予调用Lambda的权限，可以通过以下步骤完成：

1. 创建一个IAM角色，用于给CloudWatch授予调用Lambda函数的权限。可以使用以下CloudFormation模板，在IAM角色中添加所需的权限：

Resources:
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: LambdaExecutionRole
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Principal:
              Service: cloudwatch.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
        - arn:aws:iam::aws:policy/service-role/CloudWatchEventsFullAccess
        - arn:aws:iam::aws:policy/AWSLambda_FullAccess
        - arn:aws:iam::aws:policy/AWSLambda_InvokeFunction

2. 创建一个Lambda函数，用于处理CloudWatch事件。可以使用以下CloudFormation模板，在Lambda函数中添加所需的代码逻辑：

Resources:
  MyLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: MyLambdaFunction
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Runtime: python3.8
      Code:
        ZipFile: |
          import json
          def handler(event, context):
              # Add your code logic here
              return {
                  'statusCode': 200,
                  'body': json.dumps('Hello from Lambda!')
              }

3. 创建一个CloudWatch事件规则，用于触发Lambda函数。可以使用以下CloudFormation模板，在CloudWatch事件规则中设置触发条件和目标Lambda函数：

Resources:
  MyCloudWatchEventRule:
    Type: AWS::Events::Rule
    Properties:
      Name: MyCloudWatchEventRule
      Description: Trigger Lambda function on CloudWatch event
      EventPattern:
        source:
          - aws.cloudwatch
        detail-type:
          - 'Scheduled Event'
      State: ENABLED
      Targets:
        - Arn: !GetAtt MyLambdaFunction.Arn
          Id: TargetLambdaFunction

4. 将以上CloudFormation模板保存为一个.yml文件，然后使用AWS CloudFormation服务创建一个堆栈，将该模板上传并部署到AWS账号中。

通过以上步骤，您将成功使用AWS CloudFormation为CloudWatch授予调用Lambda的权限，并创建一个能够处理CloudWatch事件的Lambda函数。