I had this flower for 4 years. It used to bloom in the first 2 years but now it doesn't. Can anyone help me know what kind of flower it is and how should I take care of it. Thank you
Your plant is a Kalanchoe - because it's not in flower, I'll assume its Kalanchoe blossfeldiana, since the foliage indicates that variety. The flowers can be various colours, red, yellow, orange and so on, see here http://www.plantsrescue.com/kalanchoe-blossfeldiana/
Yours is looking very healthy, but regardless, it can be difficult persuading them to bloom again. The advice in my Houseplant Expert book is to prune back the tops after flowering, place on a shady windowsill, keep the potting soil almost dry for a month, and then put in a well lit spot (east or west facing window, or south in the winter) and water normally in order to encourage blooming. I know it hasn't flowered recently, but you could carry out this treatment now - cut back by 4- 6 inches and place it somewhere out of sunlight indoors, and keep it almost dry, then reposition in a brighter spot and water as usual.