Real time process diagnostics for reactive deposition of MgO were done to optimize high deposition rate and high transparency of the deposited films in rectangular (5 inch x 25 inch) target system. Inductively coupled plasma was adopted to enhance reactivity of oxygen for low temperature deposition of MgO. Using bipolar pulse power supply at 150 kHz, depositiion rate of 30 nm/min was achieved with 500 W pulse and 300 W of ICP power, which gave 90% of UV/VIS transparency(300 nm - 800 nm). For more intelligent feedback control, several real time diagnostics including OES, discahrge voltage and current waveform, QMS were carried out. With aid of ICP, metal ion signal showed very strong correlation with the reactivity of the plasma.