I just moved into this house when I see looks like black smoke around every heating vent in the house, What's the cause?

Could be dust and dirt accumulation from the air handler or products of combustion from a cracked heat exchanger or malfunctioning heater. Have this checked promptly as one product of combustion, Carbon Monoxide, is very dangerous.

I agree with ma. Sure sounds like a heat exchanger problem. Need to get a pro in there asap. Your life may depend on it.

I third that with EXTREME EMPHASIS on getting a QUALIFIED technician in there ASAP.

After you get the furnace checked, if all is good, and the tech can't come up with any proof that the heat exchanger has failed, and you need to start looking for other cuases, I would ask you, do you burn a lot of candles or incense on a regular basis. I only mention this because I have seen the effects of heavy candle burning, and it really can leave blackened areas where there is airflow. Now, that being said. Even if you do burn candles, you still need to have the furnace checked, no ifs and or buts about it. Safety first, right? Also, can you tell us if this is a natural gas, propane, or diesel, or (not likely) an electric unit.

Okay, there is one last option. You say you just moved into the house. Does that mean it is a brand new house, or just new to you? I will say this just for the sake of saying it. Im still not quite sure if you are seeing actuall smoke, or just blackness around the registes that you assume is left by smoke. If you are seeing actuall smoke, it may be due to a new furnace burning off factory residue, but that usually comes with a pretty strong smell, and disipates within a few hours of new furnace operation. Im really curious about your situation, and am hoping you will come back and let us know what is found. There are definitely a few options here, but I stress again, as have the above posters, get that unit checked first and foremost.