Currently solar photovoltaic that is integrated into the gridhas significantly increased the capacity. High photovoltaic penetration on the grid has an effect on the reliability and stability system. This is due to the nature of the fluctuative photovoltaic generation. This paper analyzed the effect of fluctuative photovoltaic generation on system frequency and determined the maximum level of photovoltaic penetration integrated to a 20 kV distribution grid which is in accordance with Indonesian grid code. A matlab simulink is used to simulate the solar photovoltaic integrated into the distribution grid which the photovoltaic penetration are varied to be 25%., 20%., 15% and 10% of peak load. In this simulation., the photovoltaic plant is not equipped by energy storage system that aim to see the frequency response system naturally. One of the grid code that must be complied is to keep the frequency system in the range of 47.5 to 52 Hz. Based on the simulation., photovoltaic penetration of 25% results the lowest frequency of 46.6 Hz so that the penetration is not permitted to integrate into the grid. While the maximum level of photovoltaic penetration that might be allowed to integrate is 20% which results in the lowest frequency of 48 Hz.