In this article, the performance of the multiple-input multiple-output (MIMO) based free space optical (FSO) link is analyzed with Gamma-Gamma (GG) distribution in terms of Bit Error Rate (BER). The solution for the GG distribution with MIMO leads to complexity as it involves Meijer-G function. To reduce the complexity, we propose a mathematically tractable power series based probability density function (PDF) of the GG fading with Pointing Errors (PEs) and Atmospheric Turbulences (ATs). With the proposed PDF the exact BER is derived and the performance of the MIMO link with M-ary Phase Shift Keying (M-PSK) is analyzed in terms of BER and SNR. The maximal ratio combining (MRC) provides high SNR gain of 3. 5dB over equal gain combining (EGC) and 8dB SNR gain over selection combining (SC) for negligible PEs in=11.23 at BER 10-6. The proposed power series based PDF offers high SNR gain and power efficiency of the MIMO/FSO link over SISO and SIMO link. © 2021 IEEE.