the_excerpt()

You can redefine the length of the_excerpt() with the following filter:

function custom_excerpt_length( $length ) {
	return 60;
}
add_filter( 'excerpt_length', 'custom_excerpt_length');

source

Is this function in function.php?

please refer to the codex. it’s located in wp-includes/post-template.php.

Is this function in function.php?

no;

you need to add the code into functions.php of your theme.

Thanks you so much!!!!

Oops, yes in the functions.php. misread ??

I put it in pos-template and work very well ??