x轴缩放：
CABasicAnimation *theAnimation;
theAnimation=[CABasicAnimation animationWithKeyPath:@"transform.scale.x"];
theAnimation.duration=8;
theAnimation.removedOnCompletion = YES;
theAnimation.fromValue = [NSNumber numberWithFloat:1];
theAnimation.toValue = [NSNumber numberWithFloat:0.5];
 [yourView.layer addAnimation:theAnimation forKey:@"animateTransform"];

y轴缩放：
CABasicAnimation *theAnimation;
theAnimation=[CABasicAnimation animationWithKeyPath:@"transform.scale.y"];
theAnimation.duration=8;
theAnimation.removedOnCompletion = YES;
theAnimation.fromValue = [NSNumber numberWithFloat:1];
theAnimation.toValue = [NSNumber numberWithFloat:0.5];
 [yourView.layer addAnimation:theAnimation forKey:@"animateTransform"];

x轴，y轴同时按比例缩放：
CABasicAnimation *theAnimation;
theAnimation=[CABasicAnimation animationWithKeyPath:@"transform.scale"];
theAnimation.duration=8;
theAnimation.removedOnCompletion = YES;
theAnimation.fromValue = [NSNumber numberWithFloat:1];
theAnimation.toValue = [NSNumber numberWithFloat:0.5];
 [yourView.layer addAnimation:theAnimation forKey:@"animateTransform"];

以上缩放是以view的中心点为中心缩放的，如果需要自定义缩放点，可以设置卯点：
//中心点
[yourView.layer setAnchorPoint:CGPointMake(0.5, 0.5)];

//左上角
[yourView.layer setAnchorPoint:CGPointMake(0, 0)];

//右下角
[yourView.layer setAnchorPoint:CGPointMake(1, 1)];