Is it possible to use solar cell to provide a steady output voltage to keep motor continuously running without using battery? can voltage regulator do the job? what circuit do i need? any suggestion?

 

Of course the motor will run continuously when the sun is shining.

 

Specify what the load is, along with the required motor current and voltage. In the US, you'll get an effective 150-300 W/m^2 for incoming power; this has to be multiplied by the efficiency of the solar cells. If you figure a solar cell is roughly 1/4 efficient, then you're looking at being able to get 40-75 W/m^2 of effective power. Clearly, to answer your question, one would have to know the power consumption of the motor under load. Otherwise, your question is like "How long is a piece of rope?"