In this paper we report efficient growth of well-aligned multi-walled carbon nanotube (MWNT) forest by chemical vapor deposition (CVD). Under optimized parameters, the growth rate can be 15 microm/min and the average diameter is about 10 nm. Large photocurrent can be generated in a bundle of MWNT using camera flash. The photocurrent depends linearly on the light intensity. We propose that photon induced electron-hole pair generation in multi-walled carbon nanotubes and subsequent charge separation across the Schottky barrier is the main origin of the photocurrent.