Can a 31year old male loose weight by walking alone who 160 pounds loose 20 pounds?

Weight loss: It is possible to lose weight with walk, but you will have to walk a lot. 1 hour of walking at an average pace only burns 200 calories (1 can of coke!) which means 0.5 pounds a week. Cutting down on what you eat is more effective. Keep a log of what you eat and try to cut out sugary drinks if you haven't already. Be sure to get your thyroid checked to make sure you're at goal.

Unlikely: You would lose this weight by walking alone unless you walked for a very long time (hours and hours at a time). Your best bet is combining exercise with dietary changes. However if you are only 160 lbs you may be within normal weight for your height (without you listing your height I can't be sure).