Dear Sir or Madam:
(第一段先表明写信的目的)
I am very pleased to write this recommendation for Zhang San (张三）one of my favorite students, so as to support his application for admission into the master program.
(第二段写你们认识的过程，或你对他的看法，主要想表达的意思是，你和他很熟，说的都是真的）
The first time I met Zhang was in the course of the Pyrotechnic and Propellant. Zhang always sat in the frontrow and actively discussed with me after class, he exhibited a keenly whetted mind during discussions, the attitude and ability help him to get an A grade for scoresof 94. At the end of the course, I served as his supervisorin the Curriculum Design of the Pyrotechnic and Propellant. He impressed me in the process of the Curriculum Design, he could make a good schedule, keptin touch with me, communicated and gave a summarization every day. He summarized the advantages and disadvantages of all airbags existed in the course, made many experiments, and finally put forward a new formula. He and their group also proposed a method to reduce the traffic accident by adding sensors to identify the driver’s facial expressions during driving, then the sensors will trig the airbag or alarm before the accident.
（第三段是总结，一是对学生评价的总结，二是再次表明你的意图）
In my experience with Zhang San I was impressed with not only his extraordinary intelligence but also his ambitions and persistence, he maybe not a genius, but is the hardest one. I am sure that Zhang will be an outstanding student in the future. Thus, I would like to support him firmly in his quest recommendation into account when considering his application. I would greatly appreciate it you decide to accept him as he wishes. Please do not hesitate to contact me if I can be of further assistance.
Best Regards!
某某（你的大名）