is html/php suited for making an accounting software?
looking forward for your recommendations.thanks

Software is the wrong word to use when you're talking about HTML and PHP. Using those two things, we build what are called "Web Applications" rather than software.

If you're looking to build software, the beginner's path to take would be either Java or C#.

PHP is a C++ like object-oriented programming language with HTML capabilities that make it suitable for web-based software. It runs on the web server (Apache, et al), so it can be more secure, yet when it emits html, javascript, etc, those parts run on the client (browser). I actually used it to write a complete cell phone emulator when I was at Nokia for testing our performance monitoring tools.

So, the short answer is yes. It has the ability to interface to relational databases such as MySQL, Postgres, Oracle, etc. for data storage/retrieval capabilities which would be necessary for applications such as accounting software. This isn't to suggest that it would be a trivial exercise... :-)