Is my fast valid if I drive 300km away from home in the morning and come back in the evening. My work is like this but I don't drive every day, its may be once in 10 days

One must not be a frequent traveller (kathīr al-safar). [The frequent traveller is of two kinds:] (1) someone whose profession is travelling – such as a driver and the captain of a ship, or a delivery person or shepherd – and (2) someone who travels frequently even though his work does not require him to do so – such as someone who travels three days in a week even if it is for recreational and touristic purposes – such a person must perform tamām prayers.

In your case as you said you travel 3-4 time in a month or after every 10 days so you are not amongst frequent traveler therefore,If you are traveling after ẓuhr, you must, based on obligatory precaution, complete your fast of that day; but if you are traveling before ẓuhr, then based on obligatory precaution you cannot fast on that day, particularly if you have made the intention to travel the night before. But make sure in that case when you are traveling before Zohr prayer you must not do anything that invalidates (makes batil) a fast before reaching the permitted limit (an outskirts of your city where you live called ḥadd al-tarakhkhuṣ), otherwise kaffārah becomes obligatory on you.