To reach means to arrive at the same destination at something else, so the thing you are reaching is usually stationary To catch up means you arrive at the same destination, but that thing is moving (or was moving previously) so it's usually used for a person. e.g my friend was watching ahead but I caught up with her' 'The train is far a ahead, but if you drive fast you can catch up with it' They also have other meanings though, but I'm assuming these are the meanings you are talking about :) To reach can also mean if you stretch to be able to pick something up, e.g something on a high shelf, or across the table and catch up can also mean 'catch up with a friend' as in, you didn't talk to them for a while so you talk to them about what they have been doing recently