I just joined a new team as scrum master and I have observed team has forecast 35 effort points in every sprint and they are delivering more than 50 points . I feel there is some problem with estimates. I need to make sure that estimates should be not very high . Is there any way to control this ?
What you need to do is document the facts.
Keep a clear record of the forecasts for each sprint and the actual deliveries.
Make sure you have dates for each fact.
Once you have a few weeks worth of data then you can approach the scrum master and ask them to explain their methods of estimation and suggest ways to improve it.
You cannot expect to change anything by making claims of what you seem to observe as a newcomer unless you have it clearly documented.
You may also want to find out if you can get to some historical data; possibly the past few weeks have been special circumstances that you aren't aware of, and usually, they are better at estimating.
You can also shadow them by running a parallel (hidden) system with your estimates and show them - after a few weeks - how you approach is better.
Is this regular? As in more than 5 sprints in a row? If yes, then you should help the team improve their estimation. And this is to ensure that they are fully capable of estimating properly.
If they are still estimating higher than expected, that's a good thing. This means you have enough buffer to deal with unplanned problems like additional work, change in scope etc. Just make sure, it is because they underestimate their own skill level and not because they are incapable of correct estimation. Because the latter will cause problems some day.